A comparative investigation on the microstructure and mechanical properties of additively manufactured aluminum alloys

Due to exceptional strength/stiffness to weight ratio, aluminum (Al) alloys are being extensively used in many exclusive applications. The microstructure, and consequently, the mechanical properties of additively manufactured (AM) Al alloys are expected to vary compared to those of their conventionally manufactured counterparts due to the unique thermal history experienced during the additive manufacturing (AM) processes. Therefore, it is critical to understand the microstructure and characterize the mechanical properties of AM Al alloys to verify if they meet the requirements for being deployed in the fatigue critical applications. In this study, the microstructure and mechanical properties (i.e., tensile and fatigue) of laser beam powder bed fused (LB-PBF) LPW AlSi10Mg, EOS AlSi10Mg, Scalmalloy, and QuesTek Al alloys are characterized. Room temperature quasi static tensile tests are conducted at the strain rate of 0.001 s(-1) on machined surface specimens, and uniaxial fully-reversed strain-controlled fatigue tests are performed on both as-built and machined surface specimens. Some differences in microstructure and tensile properties of the LB-PBF AlSi10Mg fabricated with LPW and EOS powders are noticeable. Among the Al alloys, the LB-PBF Scalmalloy possesses the highest strength and high ductility as well as the highest fatigue resistance credited to its ultrafine/nano-size grains and precipitates. For all the LB-PBF Al alloys investigated, surface micro-notches and volumetric defects (pores, lack of fusion) are found to be the primary sources of fatigue crack initiation in the as-built and machined surface conditions, respectively.

Automated summary

This study characterizes the microstructure and mechanical properties of various aluminum alloys fabricated through additive manufacturing, finding that LB-PBF Scalmalloy exhibits the highest strength and fatigue resistance. Surface micro-notches and volumetric defects are identified as the primary sources of fatigue crack initiation in the investigated alloys.