Effect of La on hot cracking susceptibility of Al-Cu-Mg alloy

Abstract

Aluminum-copper alloys have wide crystallization range, leading to a strong hot cracking tendency because of dendrites and mushy solidification characteristics. In this study, the effect of La content (0–0.5 wt%) on the hot cracking susceptibility of Al-Cu-Mg alloy (Al-4.4Cu-1.5Mg-0.15Zr) was investigated. Results show that the grains size is nearly 160 ± 2 μm in La-free alloy with inhomogeneous structure. With the addition of La into alloy (0.1–0.3 wt%), grains size decreased from 120 ± 2 μm to 67 ± 2 μm and the morphology of grains gradually changed from dendrite to equiaxed crystal. The grains size was 40 ± 2 μm in La-0.4 wt% alloy with uniform equiaxed grains. When the addition of La element continued to increase to 0.5 wt%, the grain size increased to 80 ± 2 μm. Hot cracking sensitivity coefficient of the alloy is related to La content. The alloy with La-0.4 wt% represented good hot cracking resistance and mechanical properties. The hot cracking mechanisms of the alloys are discussed in detail, based on liquid film theory and solidification shrinkage compensation theory.