Influence of powder surface chemistry on the defect formation in AlSi10Mg alloy processed via laser powder bed fusion additive manufacturing

Abstract

In laser powder bed fusion(LPBF) additive manufacturing(AM) of Al alloys, surface chemistry and dissolved gas composition(oxygen/oxides/hydroxides, hydrogen and moisture) of AM powders is a major influencing factor for porosity formation. Therefore, in the present investigation, this aspect is addressed using two sets of virgin AM AlSi10Mg powders, namely, Hi-Ox (2770 ppm oxygen) and Lo-Ox (660 ppm oxygen), to assess the printability under various processing parameters and defect formation in printed parts. Comprehensive and in-depth metallurgical analysis of both powders utilizing multiple characterisation techniques established the presence of various types of oxides/hydroxides with different complex chemistries on the powders’ surface. Enhanced spherical gas porosity and oxide inclusions were witnessed in Hi-Ox print coupons in contrast to the least defects in Lo-Ox coupons rationalized due to surface chemistry difference between the virgin powders. Consequently, the mechanical properties of the Hi-Ox print coupons, even with minimum defect density, are significantly inferior to Lo-Ox specimens. These observations suggest a competing influence of surface chemistry/dissolved gas composition and laser parameters for the processing of both powders. Overall, by correlating the microstructures with processing conditions and oxide concentration, defects morphology, the probable melt pool formation mechanism in LPBF of AlSi10Mg alloy (for high and low oxygen concentration) is elucidated.