CEN/TR 16749:2014
(Main)Aluminium and aluminium alloys - Classification of Defects and Imperfections in High Pressure, Low Pressure and Gravity Die Cast Products
Aluminium and aluminium alloys - Classification of Defects and Imperfections in High Pressure, Low Pressure and Gravity Die Cast Products
This Technical Report specifies the classification of the defects and imperfections may be present in cast products manufactured by high pressure, low pressure and gravity die casting of aluminium alloys.
Aluminium und Aluminiumlegierungen - Klassifikation von Fehlern und Unvollkommenheiten für Druckguss, Niederdruckguss und Schwerkraftkokillenguss
Aluminium et alliages d'aluminium - Classification des défauts et imperfections des produits moulés par coulée à haute pression, basse pression et gravité
Aluminij in aluminijeve zlitine - Razvrstitev pomanjkljivosti in napake v visokotlačnih, nizkotlačnih in težnostno kokilno ulitih ulitkih
To tehnično poročilo določa razvrstitev napak in pomanjkljivosti, ki so lahko prisotni v visokotlačnih, nizkotlačnih in težnostno kokilno ulitih ulitkih iz aluminijevih zlitin.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-januar-2015
$OXPLQLMLQDOXPLQLMHYH]OLWLQH5D]YUVWLWHYSRPDQMNOMLYRVWLLQQDSDNHY
YLVRNRWODþQLKQL]NRWODþQLKLQWHåQRVWQRNRNLOQRXOLWLKXOLWNLK
Aluminium and aluminium alloys - Classification of Defects and Imperfections in High
Pressure, Low Pressure and Gravity Die Cast Products
Aluminium und Aluminiumlegierungen - Klassifikation von Fehlern und
Unvollkommenheiten für Druckguss, Niederdruckguss und Schwerkraftkokillenguss
Aluminium et alliages d'aluminium - Classification des défauts et imperfections des
produits moulés par coulée à haute pression, basse pression et gravité
Ta slovenski standard je istoveten z: CEN/TR 16749:2014
ICS:
77.120.10 Aluminij in aluminijeve zlitine Aluminium and aluminium
alloys
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
TECHNICAL REPORT
CEN/TR 16749
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
October 2014
ICS 77.120.10
English Version
Aluminium and aluminium alloys - Classification of Defects and
Imperfections in High Pressure, Low Pressure and Gravity Die
Cast Products
Aluminium et alliages d'aluminium - Classification des Aluminium und Aluminiumlegierungen - Klassifikation von
défauts et imperfections des produits moulés par coulée à Fehlern und Unvollkommenheiten für Druckguss,
haute pression, basse pression et gravité Niederdruckguss und Schwerkraftkokillenguss
This Technical Report was approved by CEN on 9 September 2014. It has been drawn up by the Technical Committee CEN/TC 132.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2014 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16749:2014 E
worldwide for CEN national Members.
Contents Page
Foreword . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Classification of defects and imperfections in high pressure, low pressure and gravity
die cast products . 8
4.1 General . 8
4.2 Classification . 9
5 Definition of defects and imperfections . 10
5.1 General . 10
5.2 Shrinkage defects and imperfections . 11
5.3 Gas-related defects and imperfections . 11
5.4 Filling-related defects and imperfections . 12
5.5 Undesired phases . 12
5.6 Thermal contraction defects and imperfections . 12
5.7 Metal-die interaction defects and imperfections . 13
5.8 Geometrical defects and imperfections . 13
Annex A (informative) Description of defects and imperfections in High Pressure, Low Pressure
and Gravity Die Cast Products . 14
A.1 Internal defects and imperfections . 14
A.1.1 Shrinkage defects and imperfections . 14
A.1.1.1 Macro-shrinkage (Type A1.1) . 14
A.1.1.2 Interdendritic shrinkage (Type A1.2) . 14
A.1.1.3 Layer porosity (Type A1.3) . 15
A.1.2 Gas-related defects and imperfections . 16
A.1.2.1 Air entrapment porosity (Type A2.1) . 16
A.1.2.2 Hydrogen porosity (Type A2.2) . 17
A.1.2.3 Vapor entrapment porosity (Type A2.3) . 18
A.1.2.4 Lubricant/release agent entrapment porosity (Type A2.4). 18
A.1.3 Filling-related defects and imperfections . 19
A.1.3.1 Cold joint (Type A3.1). 19
A.1.3.2 Lamination (Type A3.2) . 20
A.1.3.3 Cold shot (Type A3.3). 20
A.1.4 Undesired phases . 21
A.1.4.1 Inclusion (Type A4.1) . 21
A.1.4.2 Undesired structure (Type A4.2) . 21
A.1.5 Thermal contraction defects and imperfections . 22
A.1.5.1 Cold crack (Type A5.1) . 22
A.1.5.2 Hot tear, hot crack (Type A5.2) . 23
A.2 Surface defects and imperfections . 24
A.2.1 Shrinkage defects and imperfections . 24
A.2.1.1 Sink (Type B1.1) . 24
A.2.2 Gas-related defects and imperfections . 25
A.2.2.1 Blister (Type B2.1) . 25
A.2.2.2 Pinhole (Type B2.2) . 25
A.2.3 Filling-related defects and imperfections . 26
A.2.3.1 Cold joint and vortex (Type B3.1) . 26
A.2.3.2 Lamination (Type B3.2) . 27
A.2.3.3 Cold shot (Type B3.3). 27
A.2.4 Undesired phases . 28
A.2.4.1 Surface deposit (Type B4.1) . 28
A.2.4.2 Contaminant or inclusion (Type B4.2) . 28
A.2.5 Thermal contraction defects and imperfections . 29
A.2.5.1 Cold crack (Type B5.1) . 29
A.2.5.2 Hot tear, hot crack (Type B5.2) . 30
A.2.6 Metal/die interaction defects and imperfections . 30
A.2.6.1 Erosion (Type B6.1) . 30
A.2.6.2 Soldering (Type B6.2). 31
A.2.6.3 Thermal fatigue marks (Type B6.3) . 31
A.2.6.4 Ejection mark (Type B6.4) . 32
A.2.6.5 Corrosion of the die (Type B6.5) . 32
A.3 Geometry defects and imperfections . 33
A.3.1 Lack of material - Incompleteness (Type C1.1) . 33
A.3.2 Excess of material - Flash (Type C2.1) . 33
A.3.3 Out of tolerance - Deformation (Type C3.1) . 34
Annex B (informative) Translations of defects and imperfections terminology . 35
Annex C (informative) Examples of detection techniques and size of defects and imperfections . 37
Bibliography . 39
Foreword
This document (CEN/TR 16749:2014) has been prepared by Technical Committee CEN/TC 132 “Aluminium
and aluminium alloys”, the secretariat of which is held by AFNOR.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
1 Scope
This Technical Report specifies the classification of the defects and imperfections may be present in cast
products manufactured by high pressure, low pressure and gravity die casting of aluminium alloys.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
EN 12258-1:2012, Aluminium and aluminium alloys - Terms and definitions - Part 1: General terms
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 12258-1:2012 and the following
apply.
3.1
casting process
process in which molten metal is introduced into a mould where it solidifies
[SOURCE: EN 12258-1:2012, 3.1.1]
3.2
die casting process
casting process in which molten metal is injected under substantial pressure, typically above 70 bars, into a
metal die and solidifies under this pressure
Note 1 to entry: Die casting process is also referred to as “pressure die casting (process)” or “high pressure die
casting (process)”.
[SOURCE: EN 12258-1:2012, 3.1.10]
3.3
permanent mould casting process
casting process in which molten metal is introduced by gravity or low pressure into a mould constructed of
durable material, typically iron or steel
Note 1 to entry: A permanent mould casting process where the metal solidifies in a metal mould under low pressure
(typically less than 1 bar above atmospheric pressure) is also referred to as a “low pressure die casting process”.
[SOURCE: EN 12258-1:2012, 3.1.9]
3.4
casting
product at or near finished shape, formed by solidification of the metal in a mould or a die
[SOURCE: EN 12258-1:2012, 2.5.1]
3.5
dendrite
crystal that has a tree-like, branching pattern, being most evident in cast metals slowly cooled through the
solidification range
[SOURCE: EN 12258-1:2012, 4.5.17]
3.6
microstructure
structure of a metal as revealed by microscopic examination of a surface, typically after mechanical and/or
chemical preparation, e.g. polishing and micro-etching
[SOURCE: EN 12258-1:2012, 4.5.10]
3.7
dendrite arm spacing
mean distance of adjacent secondary arms of a dendrite
[SOURCE: EN 12258-1:2012, 4.5.18]
3.8
defect
quality characteristic which is lower with respect to the level or state foreseen (usually specified) and which
does not allow the product to carry out a function requested
[SOURCE: EN 12258-1:2012, 7.1.2]
3.9
imperfection
quality characteristic which is for a some extent lower with respect to the level or state foreseen or a
deviation from a continuous appearance of the base material not yet evaluated against a threshold level (a
technical OK / not OK evaluation is not allowed)
Note 1 to entry: The term “inhomogeneity” can also be used.
Note 2 to entry: This does not mean necessarily that the product is not suitable for use. An imperfection needs to be
evaluated by means of a proper scale, based on the related specifications, to decide if the product has a quality level
making it suitable for the use.
3.10
shrinkage cavity
void left in cast metals as a result of solidification shrinkage
[SOURCE: EN 12258-1:2012, 5.2.10]
3.11
gas porosity
porosity caused by entrapped gas, evolution by evaporated organic release compounds, or by evolution of
dissolved hydrogen during solidification
3.12
inclusion
extraneous material accidentally entrapped into the liquid metal and whose possible root causes are melt
treatment procedures initiating oxidation, transported to the melt by contaminated ingot surfaces, transported
into castings due to abrasion of process equipment, entrapped into the metal surface during hot or cold
working
3.13
blister
raised spot whose inside is hollow, that forms on the surface of products and is caused by the expansion of
entrapped gas at the opening of the die or during conditions of elevated temperature in subsurface regions,
typically during thermal treatment
3.14
hot crack
crack formed in a cast metal or in a welding because of internal stress developed upon cooling at the solidus
temperature or slightly above
[SOURCE: EN 12258-1:2012, 5.2.8]
3.15
cold crack
crack in cast metal initiated by mechanical stresses at temperatures significantly below the solidus
temperature
[SOURCE: EN 12258-1:2012, 5.2.9]
3.16
corrosion
deterioration of a metal by chemical or electrochemical reaction with its environment
[SOURCE: EN 12258-1:2012, 5.6.14]
3.17
flash
thin protrusion into the parting surface of a die which forms when metal, in excess of that required to fill the
impressions, is forced between the die interfaces
4 Classification of defects and imperfections in high pressure, low pressure and
gravity die cast products
4.1 General
Defects and imperfections implemented in the present classification are metallurgy-related, i.e. directly
bound to high pressure, low pressure and gravity die casting processes.
The defects and imperfections are classified using a scheme based on three levels:
a) The level I is based on morphology/location of defects and imperfections, with reference to the
investigation techniques suitable for their detection (visual inspections and controls involving the bulk
material): there are internal (Table 1) and external or surface (Table 2) defects and imperfections. Sub-
surface defects and imperfections (i.e. so close to the surface that they can affect external aspect
detectable by conventional surface investigation techniques) are considered surface defects and
imperfections. Finally, the geometrical defects and imperfections (Table 3) refer to the casting shape in
terms of dimensions and tolerances.
b) The level II is mainly focused on the metallurgical, physical, chemical and process-based origin of
defects and imperfections. They are grouped into several classes according to their general
metallurgical origin:
1) defects and imperfections related to the presence of gas (gas-related defects and imperfections);
2) defects and imperfections related to material volume contraction during metal solidification
(shrinkage defects and imperfections);
3) defects and imperfections related to thermal contraction prevented by previously solidified metal or
by the die (thermal contraction defects and imperfections);
4) defects and imperfections related to incorrect filling of the die-cavity (filling defects and
imperfections);
5) defects and imperfections related to metal/die interaction;
6) defects and imperfections related to the presence of unsuitable phases (undesired phases),
originating from the interaction of the metal with external environment during melting, pouring,
casting, filling or extraction/ejection from the die.
As previously observed, the knowledge of metallurgical origin could supply starting points for corrective
actions (e.g. on process parameters).
c) The level III is used to identify the specific types of defects and imperfections. Usually, the term adopted
to describe a particular type of defect and imperfection allows a better definition of its metallurgical
origin, which was preliminarily identified in the previous level.
NOTE Other defects and imperfections, related to subsequent operations (handling finishing, machining), have not
been considered.
4.2 Classification
Table 1 — Classification of internal defects and imperfections
Level I Level II Level III
A1.1 Macro-shrinkage
Shrinkage
A1 A1.2 Interdendritic shrinkage
defects and imperfections
A1.3 Layer porosity
A2.1 Air entrapment porosity
A2.2 Hydrogen porosity
Gas-related
A2
A2.3 Vapour entrapment porosity
defects and imperfections
A
Lubricant and/or die release
A2.4
Internal
agent entrapment porosity
defects and
A3.1 Cold joint
imperfections
Filling-related
A3 A3.2 Lamination
defects and imperfections
A3.3 Cold shot
A4.1 Inclusion
A4 Undesired phases
A4.2 Undesired structure
A5.1 Cold crack
Thermal contraction
A5
defects and imperfections
A5.2 Hot tear, hot crack
Table 2 — Classification of surface defects and imperfections
Level I Level II Level III
Shrinkage
B1 B1.1 Sink
defects and imperfections
B2.1 Blister
Gas-related
B2
defects and imperfections
B2.2 Pinhole
B3.1 Cold joint, Vortex
Filling-related
B3 B3.2 Lamination
defects and imperfections
B3.3 Cold shot
B
B4.1 Surface deposit
Surface
B4 Undesired phases
B4.2 Contamination, inclusion
defects and
imperfections
B5.1 Cold crack
Thermal contraction
B5
defects and imperfections
B5.2 Hot tear, hot crack
B6.1 Erosion
B6.2 Soldering
Metal-die interaction
B6 B6.3 Thermal fatigue marks
defects and imperfections
B6.4 Ejection mark
B6.5 Corrosion of the die
Table 3 — Classification of geometrical defects and imperfections
Level I Level II Level III
C C1 Lack of material C1.1 Incompleteness
Geometrical
C2 Excess material C2.1 Flash
defects and
imperfections
C3 Out of tolerance C3.1 Deformation
5 Definition of defects and imperfections
5.1 General
A short definition of each defect and imperfection is given here. Internal and surface defects and
imperfections are grouped on the basis of the phenomena generating them (shrinkage, gas entrapment or
development, filling, formation of undesired phases, thermal contraction, metal-die interaction).
Extended definitions, as well as morphology and metallurgical origin descriptions and representative
figures/schemes for each defect and imperfection are given in Annex A, as well as possible detection and
investigation methods.
Annex B collects the translations of defects and imperfections terminology from English to Italian, French,
German and Spanish languages.
Annex C reports, for each defect and imperfection, the typical size and the main detection techniques.
5.2 Shrinkage defects and imperfections
— Macro-shrinkage (A1.1)
A relatively large shrinkage cavity with irregular shape formed inside a hot spot due to the volume
contraction when liquid metal transforms into solid and not enough liquid metal flows to contrast it.
— Interdendritic shrinkage (A1.2)
Several cavities located in interdendritic regions formed when the liquid flow in the mushy zone is inadequate
to counterbalance the metal shrinkage.
— Layer porosity (A1.3)
Particular case of shrinkage cavities aligned along a specific surface; typically such surface corresponds to
the neutral thermal axis/surface of the casting.
— Sink (B1.1)
A surface depression related to the presence of a sub-surface shrinkage porosity. The thin metal layer above
is not able to sustain stress arising from the contraction of the internal region and from the surrounding
pressure, and it plastically deforms.
5.3 Gas-related defects and imperfections
— Air entrapment porosity (A2.1)
Small cavities formed as consequence of the presence of air bubbles trapped inside liquid metal. They
appear as spherical or ellipsoidal cavities characterized by relatively smooth surface.
— Hydrogen porosity (A2.2)
Due to the abrupt reduction of atomic hydrogen solubility in the solid phase, the dissolved hydrogen
recombinate to form small cavities with smooth and not oxidized surface.
— Vapor entrapment porosity (A2.3)
Cavities similar to air entrapment porosity caused by residual humidity on the die surface.
— Lubricant/release agent entrapment porosity (A2.4)
Cavities similar to air entrapment porosity caused by decomposition gases of lubricant and/or die release
agent that remain trapped into liquid metal in form of bubbles.
— Blister (B2.1)
Small surface areas which blow up if internal pressure of sub-surface gas related porosity is high enough (it
increases with temperature) to plastically deform the metal skin that covers it. It is caused by the expansion
of entrapped gas at the opening of the die or during conditions of elevated temperature in subsurface
regions, typically during thermal treatment.
— Pinhole (B2.2)
Rounded cavity usually smooth-walled of varied size, isolated or grouped irregularly, located on the surface
or in sub-surface regions, and due to gas rising from core materials.
5.4 Filling-related defects and imperfections
— Cold joint and Vortex (A3.1 – B3.1)
A cold joint forms when a relatively cold liquid metal flow meets another warmer flow around it and causes
different microstructures separated by a thin oxide film. A particular cold joint defect and imperfection is
vortex: a vortex forms on the surface when only one flow rolls itself up and generates a particular spiral
distribution of oxide films and microstructures. Alternative terms are cold shut and cold lap.
— Lamination (A3.2 – B3.2)
A thin surface metallic layer having at least partial separation surface from the bulk metal with imperfect
adhesion to the inner metal
It could be an internal defect and imperfection also: the lamination is partially separated by oxide films from
the metal.
— Cold shot (A3.3 – B3.3)
A small amount of metal with much finer microstructure than the surroundings zone originated from the
contact of a small portion of liquid metal with the surface of the die and rapidly solidifies.
5.5 Undesired phases
— Inclusion (A4.1 – B4.2)
Small particles or thin films of non-metallic phase, usually oxides or dross or fragments of refractory
coatings, entrapment in the casting.
— Undesired structure (A4.2)
Local zone of the casting with unsuitable structures characterized by high hardness or brittleness or higher
value of SDAS (Secondary Dendrite Arm Spacing) compared with general microstructure scale. Undesired
phases may derive from the shot sleeve as early solidified products (ESP) with an explicit coarser
microstructure, from macro-segregation of alloying elements, from treatments of molten alloy (e.g. during
refinement or modification).
— Surface deposit (B4.1)
A layer with various chemical composition, thickness and distribution that is deposited on the surface of the
casting.
5.6 Thermal contraction defects and imperfections
— Cold crack (A5.1 - B5.1)
A sharp edged, narrow opening forms at temperatures significantly below solidus temperature, where the
greater thermal contraction of the casting with respect to the die is prevented by particular part/die geometry
resulting in the stress generating usually trans-crystalline cracking. Tips of dendrites usually are not
characteristic for the cold cracks surfaces.
— Hot tear, hot crack (A5.2 - B5.2)
A discontinuity forms at high temperature (solidification range) in the solid portion of the mushy zone
originated by the thermal tension. Hot tear surface is oxidized and related to the dendritic morphology.
5.7 Metal-die interaction defects and imperfections
— Erosion (B6.1)
An excess of material on the surface of the casting that reproduces, in negative, a defect and imperfection of
the die caused by erosive phenomena.
— Soldering (B6.2)
Surface roughness or localized lack of surface material due to the formation of Al- and Fe-containing
intermetallic phases on the surface of the die.
— Thermal fatigue mark (B6.3)
Narrow reliefs with a particular pattern on the surface of the casting related to thermal fatigue damage of the
die cavity.
— Ejection mark (B6.4)
Local superficial plastic deformation that occurs during the ejection of the cast part due to the presence of an
undercut on the die.
— Corrosion of the die (B6.5)
Surface roughness of the cast product resulting from the corresponding die surface area attacked by
environment (corrosion phenomena).
5.8 Geometrical defects and imperfections
— Incompleteness (C1)
Lack of material with respect to designed cast geometry due to uncompleted filling of the die cavity.
— Flash (C2)
An excess of material that forms by liquid metal intruding into the gap formed between the separation
surfaces of different parts of the die, and that is not properly removed.
— Deformation (C3)
A geometrical non-conformity of the casting to its design geometry related for instance to the thermal
contraction during cooling.
Annex A
(informative)
Description of defects and imperfections in High Pressure, Low
Pressure and Gravity Die Cast Products
A.1 Internal defects and imperfections
A.1.1 Shrinkage defects and imperfections
A.1.1.1 Macro-shrinkage (Type A1.1)
Definition: A macro-shrinkage is a relatively large (with respect to casting thickness) shrinkage cavity, formed
inside a hot spot and due to the volume contraction during solidification [see Bibliography [8-17]].
Morphology: A macro-shrinkage is characterized by rough and spongy surfaces for the presence of
emerging dendrites as a consequence of their interrupted growth. A macro-shrinkage can reach several
millimetres in diameter (>0,5 mm). It can be detected by means of radiographic (according to EN 12681),
ultrasonic inspections and metallographic tests.
Metallurgical origin: The formation of a macro-shrinkage depends on die-filling conditions, alloy physical
properties (e.g. solidification range), geometry of the casting and process parameters.
Figure A.1 — Macrograph of macro-shrinkage
A.1.1.2 Interdendritic shrinkage (Type A1.2)
Definition: An interdendritic porosity consists of several cavities located in the interdendritic regions, and
forms when the liquid flow in these regions is inadequate to counterbalance the shrinkage of the metal during
solidification [see Bibliography [8-17]].
Morphology: The interdendritic porosity is characterized by a net of long and narrow three-dimensional
branches. The size of an interdendritic shrinkage varies between 10 and 150 µm. This defect/imperfection
can be detected by means of ultrasonic inspections and metallographic tests. Radiographic inspection
(according to EN 12681), better if equipped with high resolution facility, can also be used.
Metallurgical origin: The formation of the interdendritic porosity is favoured by a wide mushy zone, as could
be the case of wide solidification range and low temperature gradients (e.g. in the last solidified regions of a
thick casting). The interdendritic porosity could be a preferred path for gas, thus be deleterious for pressure
tightness. This defect/imperfection could also be a preferred path for crack propagation.
Figure A.2 — Metal flow around dendrites
A.1.1.3 Layer porosity (Type A1.3)
Definition: A layer porosity consists of a set of shrinkage defects/imperfections aligned typically along the
neutral thermal axis/surface of the casting in its thin regions (where the component thickness is far smaller
than the two other dimensions and the thermal gradient is lower than all adjacent points) [see Bibliography
[8-12], [15]].
Morphology: A layer porosity is made up of a set of small shrinkage cavities laying on a surface, typically the
neutral thermal one. The size of layer porosity varies between 10 µm and 100 µm. This defect/imperfection
can be detected by means of ultrasonic inspections and metallographic tests. Radiographic inspection
(according to EN 12681), better if equipped with high resolution facility, can also be used.
Metallurgical origin: The layer porosity forms when the solidification fronts converge towards two surfaces
and the last solidifying liquid metal cannot flow within the dendrites of the mushy zone.
Key
a die
α phase
Al-Si eutetic
Porosity
Figure A.3 — Formation of layer porosity
A.1.2 Gas-related defects and imperfections
A.1.2.1 Air entrapment porosity (Type A2.1)
Definition: The air entrapment porosity consists of small cavities due to air bubbles trapped inside the liquid
metal [see Bibliography [8-17]].
Morphology: Air entrapment porosities appear as spherical or ellipsoidal cavities characterized by relatively
smooth surfaces on which a thin oxide layer (due to the high-temperature interaction between air and the
liquid metal) could be found.
The final distribution of cavities within the casting depends on the path of the metal. The size of air
entrapment porosity is 10 µm - 2000 µm. This defect/imperfection can be detected by means of radiographic
(according to EN 12681), ultrasonic inspections and metallographic tests.
Metallurgical origin: Air bubbles can form in turbulent liquid metal vein either when it is in the shot sleeve, in
filling channels or inside die cavity.
Figure A.4 — Entrapped air porosity in the casting
A.1.2.2 Hydrogen porosity (Type A2.2)
Definition: The hydrogen porosity consists of cavities due to the presence of hydrogen in the melt
[see Bibliography [8-17]].
Morphology: Hydrogen porosity consists of approximately spherical cavities characterized by smooth and no-
oxidized surface. Such cavities have a rather small size (0,05 mm -0,5 mm of diameter) and are distributed
almost homogeneously within the casting. This defect/imperfection can be detected by means of
radiographic (according to EN 12681), ultrasonic inspections and metallographic tests.
Metallurgical origin: Humidity can cause the presence of monoatomic hydrogen within the liquid metal at high
temperature. Due to the abrupt reduction of hydrogen solubility in the solid phase, the solidifying region
rejects hydrogen and this element concentrates in the liquid near the liquid/solid interface, where it combines
into molecular form.
Figure A.5 — Entrapped air porosity in the casting
A.1.2.3 Vapor entrapment porosity (Type A2.3)
Definition: The vapor entrapment porosity consists of cavities caused by the residual humidity of the die.
Humidity becomes vapor when it comes into contact with the molten metal [see Bibliography [8-10], [15]].
Morphology: The vapor entrapment porosity is generally in the form of approximately spherical cavities with
smooth surfaces. Due to the generally localized presence of humidity on the die, cavities are typically
concentrated, even if in regions of the casting that could be far from the area where they originated. The size
of vapor entrapment porosity is 0,5 mm - 3,0 mm. This defect/imperfection can be detected by means of
radiographic (according to EN 12681), ultrasonic inspections and metallographic tests.
Metallurgical origin: The presence of humidity on the die surface could result from an excess of the water-
based lubricant.
Key
A residual humidity
Figure A.6 — Schematics of vapor entrapment porosity
A.1.2.4 Lubricant/release agent entrapment porosity (Type A2.4)
Definition: The lubricant/release agent entrapment porosity forms when the gases - resulting from the
decomposition of the lubricant/release agent - remain trapped into liquid metal in form of bubbles
[see Bibliography [8-10], [15]].
Morphology: The lubricant/release agent entrapment porosity is characterized by small, approximately
spherical cavities with smooth surfaces. The surface of the cavities appears darker respect to the surface of
gas-related defects/imperfections due to the presence of combustion products on it. The size of a lubricant
/release agent entrapment porosity varies between 0,5 mm and 3,0 mm. This defect/imperfection can be
detected by means of radiographic (according to EN 12681), ultrasonic inspections and metallographic tests.
Metallurgical origin: The lubricant/release agent entrapment porosity is caused by an excessive quantity of
lubricant/release agent on the die surface and/or piston/sleeve coming into contact with molten metal.
Key
A lubricant film
B gas development from lubricant
Figure A.7 — Schematics of lubricant entrapment porosity
A.1.3 Filling-related defects and imperfections
A.1.3.1 Cold joint (Type A3.1)
Definition: A cold joint is a discontinuity of metallurgical type (either microstructural and/or metallic) rather
than of geometrical-type (such as, for example, a cavity or a crack) [see Bibliography [8-10], [12-16]].
Morphology: The appearance of this defect/imperfection depends on the conditions of the metal flows at the
moment of their confluence and on their location within the die-cavity. This defect/imperfection can be
detected mainly by means of metallographic tests.
Metallurgical origin: The cold joint forms when a relatively cold liquid metal flow - at least partially solidified
and in some cases covered by an oxide film - meets another warmer metal vein that can flow around it. The
cold joint usually brakes along the previous interface of flows when relatively low tension stresses normal to
it or shear stresses parallel to it are applied.
Figure A.8 — Micrograph of a cold joint
A.1.3.2 Lamination (Type A3.2)
Definition: A lamination is a typical surface defect/imperfection (see A.1.3.1), but in some cases can be also
considered as internal defect/imperfection. The lamination is a sort of thin metallic layer (skin) with different
microstructure in comparison to the material laying around and partly separated by a thin oxide film
[see Bibliography [8-10], [12-16]].
Morphology: This defect/imperfection consists of a thin metallic layer having a separation surface from the
bulk metal almost parallel to the component surface, with imperfect adhesion to the inner metal and with finer
microstructure. This defect/imperfection presents variable size and can be detected by means of ultrasonic
inspections and metallographic tests.
Metallurgical origin: The lamination forms when the metal foil comes into contact with the die surface and
cools down with a higher rate than the surrounding regions.
Figure A.9 — Schematics of a lamination
A.1.3.3 Cold shot (Type A3.3)
Definition: Even if a cold shot always originates at the surface of the die, it can be found as internal
defect/imperfection when it is trailed by a liquid metal flow. The cold shot is a small amount of metal
characterized by microstructural features much finer than the surrounding regions and separated by a thin
oxide layer [see Bibliography [8-10], [12-17]].
Morphology: The cold shot looks like a small amount of metal with a spherical or ellipsoidal shape. The size
of a cold shot varies between 0,01 mm and 1,0 mm. This defect/imperfection can be detected only by means
of metallographic tests.
Metallurgical origin: A cold shot forms when the alloy flows turbulently with a front characterized by a
considerable presence of drops (spray effect) and comes into contact with the surface of the die
(see A.2.3.3). In such conditions, the molten metal can approach the solidus temperature and rapidly
solidifies.
Figure A.10 — Micrograph of a cold shot
A.1.4 Undesired phases
A.1.4.1 Inclusion (Type A4.1)
Definition: Inclusions are typically non-metallic phases and include oxides and dross [see Bibliography [8-
10], [12-17]].
Morphology: The inclusion can be in the form of a particle or of a thin film. The size of an inclusion is major
than 0,05 mm. This defect/imperfection can be detected by means of ultrasonic and radiographic inspections
and metallographic tests.
Metallurgical origin: In Al-alloys the most frequent type of inclusion is the aluminium oxide, i.e. alumina
(Al O ). It easily forms when the liquid metal comes into contact with air.
2 3
Inclusions can also be other non-metallic phases, such as small portions of refractories (often silicon
carbide) or dross. Because of their high hardness, inclusions can cause machining problems.
Figure A.11 — Image of aluminium oxide
A.1.4.2 Undesired structure (Type A4.2)
Definition: These are areas of different microstructure which are undesired mainly for their high hardness,
stiffness, brittleness and because they create microstructural discontinuities [see Bibliography [8-13], [15-
16]].
Morphology: The morphology of undesired structures cannot be uniquely described and their size depends
on the cell size. For example, the SDAS could be outside the acceptable limit for a specific region of the
casting. This defect/imperfection can be detected by means of metallographic tests.
Metallurgical origin: Undesired structures can include portions of previously produced castings (for example
flash), accidentally left within the die-cavity and then embedded in the successive casting.
Undesired structures represent microstructural discontinuities and could act as crack nucleation and
propagation sites during cooling, finishing operations or in-service behaviour.
Figure A.12 — Micrograph of a region with large dendrites
A.1.5 Thermal contraction defects and imperfections
A.1.5.1 Cold crack (Type A5.1)
Definition: A cold crack is a geometrical discontinuity characterized by one dimension far smaller than the
two others [see Bibliography [8-10], [12-16]].
Morphology: A narrow void volume lays within the two faced fracture surfaces which define crack. The length
of a crack varies between 10 µm to several millimetres. The surfaces often show transcrystalline failure
mode as a differentiation of hot cracks / tears. This defect/imperfection can be detected by means of
ultrasonic inspections and metallographic tests. It can be detected also by radiographic inspection, if X-Ray
shoot and hot tear have the same direction.
Metallurgical origin: Such defect/imperfection forms at relatively low temperature (far from the solidification
range) when the greater thermal contraction of the casting with respect to the die is prevented by the die
itself. Cracks can often occur in regions of stress localization, either due to macroscopic geometrical reasons
or to the presence of microstructural defects/imperfections.
Key
A crack
Figure A.13 — S
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...