Effects of powder reuse on the microstructure and mechanical behaviour of Al-Mg-Sc-Zr alloy processed by laser powder bed fusion (LPBF)

Laser powder-bed fusion (LPBF) technology is one of the additive manufacturing (AM) processes that uses metal powder to produce parts for various industry sectors such as medical, aerospace, automotive and oil & gas. As an 'additive' based process, the material is selectively melted by a focused laser. By this working principle material is added in a layer-by-layer approach only where is needed. Therefore, this technology enables a high reduction of waste by avoiding chips typically generated in 'subtractive' based processes such as milling and drilling. However, to ensure lower waste consumption the metal powder surrounding the solidified part must be reused in subsequent build jobs. Current knowledge on the effect of powder reuse on LPBF builds is mostly limited to titanium- and nickel- based alloys. The aim of this paper is to study the effect of powder reuse on Al-Mg-Sc-Zr, a high strength aluminium-based alloy, manufactured by LPBF. Here, powder properties such as morphology, composition, particle size distribution are studied of virgin (pristine) and reused Al-Mg-Sc-Zr powder. The mechanical properties of specimens made of virgin powder and after four build cycles are analysed and compared to assess the influence of a mixture of virgin and reused powder material on the consolidated material properties. In general, the powder does not present large differences in composition and morphology, only the reused powder presents coarser particle size distribution (PSD) as previously observed in other alloy compositions. The microstructure of the studied specimens is very similar unlike the porosity. The specimens built with reused powder show a few small micro-sized pores which do not show significant differences in the mechanical properties. In fact, the ultimate tensile strength (TITS) and elongation to break of specimens, respectively built with virgin and reused powder are 565 MPa, 13% and 537 MPa, 11%. Based on the obtained results, it is concluded that it is feasible to reuse Al-Mg-Sc-Zr powder in four subsequent build jobs with proper powder sieving and a rejuvenation step mixing 40% of virgin powder.