The Relationship of Microstructure to Monotonic and Cyclic Straining of Two Age Hardening Aluminum Alloys.

摘要

The effect of microstructure on the monotonic and low cycle fatigue properties of a high purity, large grain, ternary aluminum-zinc, magnesium (Al-Zn-Mg) alloy and a high strength 7050 aluminum alloy was investigated. The best combination of fatigue life, strength, and ductility for the ternary alloy resulted when aged to produce a microstructure containing predominately eta prime having a Guinier radius of approximately 65A and a small amount of incoherent eta (MgZn2). Superior fatigue life, strength, and ductility were found when the 7050 alloy was aged to produce the maximum number of partially coherent eta prime precipitates having a Guinier radius of approximately 35A. Aging the 7050 alloy to produce particles larger than 50A gave a microstructure that had lower fatigue properties at low plastic strain amplitudes. The empirical Coffin-Manson relationship was found to hold for a given deformation process; however, changes in deformation character resulted in changes in the Coffin-Manson parameters.