CONTROLLING RESIDUAL STRESS WHILE ACHIEVING DIMENSIONAL STABILITY IN ALUMINUM ALLOYS - A HISTORICAL PERSPECTIVE

摘要

Residual Stresses that can cause problems with dimensional stability in high strength aluminum alloys, have been a constant problem in the aerospace industry for many years. This problem reached its peak in the late 1960's. The results were: (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 to meet required dimensional tolerances. The stress corrosion cracking problem was a serious problem throughout the airframe industry. Planes had to be taken out of service with cracked parts, parts would crack while sitting on a shelf overnight and machining suppliers were faced with the constant problem of severe distortion during machining operations. Unfortunately, the problem continues today as (1) industry pushes the envelope toward bigger aircraft requiring larger high strength aluminum components and (2) extremely tight dimensional stability and tolerances are required in optical components such as space mirrors and telescope parts. This article summarizes over 50 years of experience in combating these problems and reviews the techniques such as cooling rate control, stress relieving methods using both mechanical and cryogenic means, and methods for controlling machining stresses. Understanding these techniques, an engineer can easily combat problems high residual stress. By combining them into an integrated systems approach, this presentation will show that any aluminum part can be produced meeting all structural requirements while at the same time be dimensionally stable resulting from the absence of a high level of residual stress.