Stress relieving of aluminium die casting
Stress relieving of aluminium die casting
(OP)
Is it possible by metallographic means, hardness or other simple test to determine whether a pressure die cast aluminium alloy has been stress relieved or not?
The material is Japanese spec ADC12 (close to AA335).
Stress relieving is done at 210 degrees C for 2 hours after die casting and cooling to room temperature.
It is thought the reason for cracks found in an automotive casting may be caused by a batch that missed heat treatment
Thanks in advance for any help received.
The material is Japanese spec ADC12 (close to AA335).
Stress relieving is done at 210 degrees C for 2 hours after die casting and cooling to room temperature.
It is thought the reason for cracks found in an automotive casting may be caused by a batch that missed heat treatment
Thanks in advance for any help received.





RE: Stress relieving of aluminium die casting
RE: Stress relieving of aluminium die casting
Thanks for your input. We have tried hardness tests, however there is no trend in hardness variation I could hang my hat on.
There is no heat treatment conducted on the part apart from the low temperature stress relieve of 210C x 2 hrs.
RE: Stress relieving of aluminium die casting
Since stress relief is the intended function, techniques used for measuring stress would be my suggestion. It may be possible to do something relatively simple like strain gauging, but x-ray diffraction is the standard method for measuring residual stress. TEC, Proto, and Stressolvers are all companies specializing in this area.
The following website has some interesting info on a recently developed technique that you may find useful:
http://www.lanl.gov/contour/
RE: Stress relieving of aluminium die casting
RE: Stress relieving of aluminium die casting
The Aluminum Association (http://www.aluminum.org) has info and plots in the quality control sections of both “Aluminum Standards and Data – 2003” and “Standards for Aluminum Sand and Permanent Mold Castings, 2000.” This is also covered in NDT books, e.g., ASM Handbook, Volume 17 “Nondestructive Evaluation and Quality Control.” http://www.asminternational.org/
Another thing you might try are before and after measurements on a part that you slice and dice. Warping would demonstrate residual stress. Measure, take a thin slice through the center using lots of coolant on the saw blade, and remeasure. Then cut a big section out of the center and measure some more.
I have a question: Are these cracks that occurred in use (under load)? If not, i.e., if the cracks were found in virgin parts, then you are looking for the wrong thing. Cracking in diecast is mostly due to hot tearing after initial solidification, while the part is still in the die. The purpose of the stress relief is to allow a) finish machining w/o distortion and b) enable handling of design loads during end use.
RE: Stress relieving of aluminium die casting
RE: Stress relieving of aluminium die casting
Kenvlach
The cracking occured during an engine durability test of a trial development part of unknown heat treatment.
We are currently trying to reproduce the failure by repeating the test.
I will try the eddy current option with known heat treated and as cast parts parts.
Thanks again
RE: Stress relieving of aluminium die casting
SAE Standard
Document Number: ARP891
Date Published: July 1976
Revision Number: A
Title: Determination of Aluminum Alloy Tempers Through Electrical Conductivity Measurements (Eddy Current)
Issuing Committee: G-3, Aerospace Couplings, Fittings, Hose, Tubing Assemblies
Scope:This recommended practice establishes a procedure for checking the tempers of aluminum alloys through eddy current conductivity measurements and defines criteria for acceptance or rejection.
Product Status: In Stock
File Size: 189K
http://www.sae.org/servlets/productDetail?PROD_TYP=STD&PROD_CD=ARP891A
Eddy current doesn't have a lot of penetrating power, but there should be a lot of residual stress in the skin layer.