Evaluation of the Effect of Rare Earth Alloying Additions on the Hot Tearing Susceptibility of Aluminum Alloy 7150 During Rapid Solidification

Abstract

Additive manufacturing of the high-strength 7xxx Al alloy series is limited due to the susceptibility of these alloys to hot tearing. The objective of the current study is to determine the effect of rare earth (RE) element additions on the hot tearing susceptibility of Al alloy 7150 during rapid solidification conditions characteristic of additive manufacturing processes. Cast 7150-xRE (x = 0, 3, 6 wt pct) samples were remelted using a number of laser power-scan speed combinations. Cracks were observed in melt pools for 6 out of 12 processing conditions for 7150, but in all 12 conditions for the RE-containing alloys. Electron backscatter diffraction of the melt pool revealed the melt pool boundary grain size increased with RE additions, and cracks occurred along the grain boundaries. RE-containing intermetallics were observed on the crack surfaces, and were noted to possibly impede the interdendritic flow of eutectic liquids. A smaller amount of eutectic was observed in the thermal data for the RE alloys compared to 7150. Hot tearing indicators were useful in understanding the effect of RE additions when coupled with the experimental results. It is concluded that the addition of 3 to 6 wt pct RE elements increases hot tearing in 7150.