Microstructural Evolution and Softening Behavior of Simulated Heat-Affected Zone in 2219 Aluminum Alloy

Abstract

The effect of peak temperature (T p) at 200, 300, 400, 500 and 550 °C on the microstructural evolution and softening behavior of the simulated heat-affected zone (HAZ) was studied in the 2219-T87 alloy by electron-backscatter diffraction, transmission electron microscopy, X-ray diffraction, micro-hardness and micro-tensile tests. The results showed that the grain size in the HAZs at 200–500 °C was comparable, but the number density of the strengthening precipitates (GP zones/θ′) decreased with increasing T p. At a T p of 550 °C, the grain size significantly decreased and the distribution of the misorientation angles corresponded to the MacKenzie distribution. The GP zones/θ′ phase coarsened and translated into θ phases at T p values in the range of 200–400 °C. Increasing the T p to 500 °C and above, some θ′ phases translated into θ phases and others dissolved into the α-Al matrix which led to an increase in the solid solution strengthening. The reduction of the number density of the GP zones/θ′ was responsible for the softening behavior.