A SYSTEMS APPROACH FOR ACHIEVING STRESS FREE PARTS IN HIGH STRENGTH ALUMINUM ALLOYS

摘要

This article presents a detailed systems approach which has been developed over the past fifty years for improving the dimensional stability of high strength aluminum alloys. It will show, with illustrations, that when applied correctly, any high strength aluminum alloy part can be produced with minimum residual stresses and optimum dimensional stability, while at the same time achieving all the structural properties desired. This development started with the severe problems of residual stress in the aerospace industry which reached its peak in the late 1960's. It was evidenced by (1) premature failure of parts in service, including both stress corrosion cracking and early fatigue failures and (2) unwanted part movement - both in service and during final machining which was being used to meet required dimensional tolerances. Unfortunately, the problem continues today as (1) the aerospace and aluminum industries push the envelope toward bigger aircraft requiring larger, high strength aluminum components and (2) extremely tight dimensional stability is required in optical components such as space mirrors. This systems approach involves a step by step procedure, which has been found to be necessary to produce stress free parts. The article will cover a fundamental understanding of the creation of high levels of residual stress in heat treated aluminum alloys as well as the integration of six critical parameters that must be understood and properly applied to achieve stress free parts -cooling rate control, proper application of mechanical, thermal and cryogenic stress relieving methods, proper control of the machining process, and the affect of other outside forces which can impart high levels of stress to the part.