The Effects of Heat Treatment on the Properties of Additively Manufactured AlSi7Mg Produced with Reused Powder

Laser powder bed fusion produces parts with low material waste; however, this relies on powder reuse. Parts manufactured with reused powder often have changed properties, with minimal research investigating the mitigation of these changes. This work, therefore, focused on the use of a T6 treatment to limit the influence of powder reuse in AlSi7Mg to provide consistent properties during manufacturing for up to 20 build cycles. The refreshing powder reuse technique was employed, with parts stress relieved or T6 treated to determine the effect of heat treatment on parts manufactured with reused powders. Minimal changes to part microstructures were observed, but stress-relieved samples saw their hardness increase by 6.0 pct and tensile strength by 7.2 pct over the first seven and nine manufacturing runs, respectively, while the yield strength, ductility, and flexural properties saw no changes. T6-treated samples saw no evolution in these properties. This was attributed to the strengthening mechanisms of these heat treatment states, where oxides in stress-relieved samples increased strengths whereas slight changes in magnesium content did not influence the strengthening from β -Mg 2 Si precipitates in T6-treated samples over the course of powder reuse, implying T6 treatment can mitigate the effects of powder reuse.