Microstructures and tensile properties of a selective laser melted Al–Zn–Mg–Cu (Al7075) alloy by Si and Zr microalloying

Abstract

The application of conventional Al–Zn–Mg–Cu alloys for selective laser melting (SLM) of additive manufacturing is hindered by hot cracking during the SLM process. In the present work, a novel Si- and Zr-modified Al–Zn–Mg–Cu (Al7075) prealloyed powder was developed for SLM, and the printability, microstructure, and mechanical properties of the as-built samples were evaluated at various laser powers. The as-built samples are completely crack-free at various laser powers, showing that Si and Zr effectively prevent hot cracking for SLM printed Al–Zn–Mg–Cu. The mechanisms of tensile property enhancement are as follows: first, the low melting point Si-rich eutectics backfill the cracks; second, the Al3Zr significantly decreases the grain sizes. The microstructure has a bipolar grain distribution with fine grains at the bottom of the melt pool (2–5 μm) and coarse columnar grains (10–30 μm) at the top of the melt pool. The synergistic effect of the Si and Zr contribute to outstanding tensile properties (446 MPa tensile strength and 6.5 % elongation), which are higher than those for SLM printed Al–Zn–Mg–Cu alloys without the addition of Si and Zr.