The influence of elevated Fe and Zn impurities on the rapid solidification behaviour of AA6061 processed using single-track laser surface melting

Abstract

Increased adoption of recycled aluminum (Al) alloys in the automotive sector can provide several economic and environmental benefits through vehicle lightweighting, decreased fuel consumption, and reduction in greenhouse gas emissions.  A major challenge in the adoption of secondary Al for a broader range of products is the accumulation of impurity elements, as increased scrap use can result in the compositional drift of alloy streams, leading to degraded mechanical and electrochemical properties. The objective of the current study is to demonstrate the use of rapid solidification processing (RSP) to increase the potential adoption of recycled Al through refinement of microstructural features and reduction of cracking. Cast ingots of an Al alloy 6061 (AA6061) were produced with iron (Fe) and zinc (Zn) additions in amounts ranging from 0 to 1 wt% to simulate recycling impurities.  Thermodynamic simulations were used to predict the crack susceptibility of each alloy composition. Laser surface melting (LSM) trials were performed on plates cut from each ingot to generate rapidly solidified microstructures. The simulation predictions and microstructure results suggest that alloy impurity composition does influence the cracking behaviour observed in the laser melt pools, with both Fe and Zn additions having a mitigating effect on the observed cracking behaviour. The results suggest that the adoption of techniques such as additive manufacturing and laser welding could enable greater use of recycled Al alloys, advancing their use for automotive applications.