Microstructural development and aging behavior of Al–Cr–Zr heat-resistant alloy fabricated using laser powder bed fusion

Abstract

Using laser powder bed fusion (L-PBF), we designed and fabricated specimens of a heat-resistant Al–4mass%Cr–1.5mass%Zr alloy (Al–4Cr–1.5Zr). The Al–4Cr–1.5Zr L-PBF specimen achieved high relative density greater than 99.9% by optimizing the laser scan conditions. The hardness and tensile and 0.2% proof stresses of the Al–4Cr–1.5Zr L-PBF specimens significantly increased after aging heat treatments, and the peak-aged specimens exhibited excellent high-temperature strength. The L-PBF specimens consisted of coarse columnar and fine equiaxed crystal grains owing to heterogeneous nucleation by the primarily crystallized Al3Zr phase. In the peak-aged L-PBF specimen, a finely dispersed Al3Zr granular phase on the order of single nanometers was precipitated in the α-Al matrix by aging. Meanwhile, the chromium was supersaturated in an α-Al solid solution even after peak aging, and partially precipitated into coarse granular Al–Cr-based compounds. These multi-scale microstructural observation results revealed that the dominant strengthening factors in the Al–4Cr–1.5Zr L-PBF specimens were precipitation hardening by the fine L12-Al3Zr phase having a strong crystallographic consistency with the α-Al matrix, solid-solution hardening with chromium, dispersion hardening due to the Al–Cr-based compounds, and hardening by the crystal grain refinement mainly with the fine equiaxed grains.