Residual Stress and Microstructural Variations in Thick Aluminium Alloy Forgings
The most critical stage in the heat treatment of high strength aluminium alloys is the rapid cooling necessary to form a supersaturated solid solution. During cold water quenching of thick sections, the thermal gradients are sufficient to cause inhomogeneous plastic deformation which in turn leads to the development of large residual stresses. Two 215 mm thick rectilinear forgings made from 7075 and 7010 were heat treated, and the through thickness residual stresses measured by neutron diffraction and deep hole drilling. The distribution of residual stresses was found to be similar for both alloys varying from highly triaxial and tensile in the core to a state of biaxial compression in the surface. The 7010 forging exhibited significantly larger tensile stresses in the core. 7075 is a much more quench sensitive alloy when compared to 7010. This results in loss of supersaturation by second phase precipitation during quenching in the core of the 7075 forging.
A. R. Pyzalla, A. Borbély and H.-P. Degischer
J. S. Robinson et al., "Residual Stress and Microstructural Variations in Thick Aluminium Alloy Forgings", Materials Science Forum, Vols. 571-572, pp. 45-50, 2008