Effects of the addition of silicon to 7075 aluminum alloy on microstructure, mechanical properties, and selective laser melting processability

Abstract

Aluminum alloys that can be processed using the selective laser melting (SLM) technique have been restricted to cast alloys based on the Al–Si binary system. To increase the selection of materials available for SLM, researches on SLM processability using wrought Al alloys (e.g. 2xxx, 7xxx series) have been conducted. The 7075 Al alloy has excellent mechanical properties among aluminum alloys; however, 7075 alloy has the problem of severe cracking occurring in parts fabricated through the SLM process. Our study demonstrated that additional silicon enables the fabrication of 7075 SLM parts without major defects and that the amount of silicon content changes the favorable processing conditions, morphology of microstructure, and mechanical properties. As the silicon content increased, voids and cracking in SLM samples were suppressed, and volumetric energy density for sufficient densification was reduced. Vickers microhardness and 0.2% proof strength were enhanced with increments of additional silicon content. In contrast, excessive silicon content resulted in brittleness, which appeared as slight ductility measured on tensile testing and breakage of samples during SLM process. These conflicting effects indicated that silicon content must be adjusted depending on the underlying alloy to yield better processability and a balance between strength and ductility. For the 7075 alloy, the optimal silicon content could be concluded to be 5%, being the lowest amount of silicon content needed for the elimination of cracking with enhanced tensile strength and acceptable ductility.