Laser Powder Bed Fusion of Crack-free 7A76 High-strength Aluminum Alloy

Laser Powder Bed Fusion (LPBF) has rapidly emerged as the leading metal additive manufacturing (AM) technology, transforming production capabilities across a range of industries. Aluminum alloys, the second most widely used structural materials, offer limited options for LPBF technique. Among them, AlSi10Mg is one of the few commercially viable choices, but its mechanical properties are relatively modest, making it less suitable for high-performance applications. Many of the most well-known high-strength Al alloys, including the 2xxx, 6xxx, and 7xxx series are prone to solidification cracking during LPBF, making them challenging in terms of printability. This limitation leaves the growing demand from aerospace and automotive sectors for robust, lightweight Al components largely unfulfilled. The addition of nanoparticles to Al alloys has emerged as a promising strategy to mitigate cracking in LPBF. This novel approach offers a potential solution to overcoming the long-standing challenges in processing high-strength Al alloys.
In this work, ZrH2 nanoparticles were added to AA7075 alloy, commercially known as 7A76 alloy to successfully eliminate solidification cracking. The AA7075 powders have been manufactured via DirectPowder™ (DP) which is a low cost, gas-free method with nearly ~3 times less energy consumption compared to gas-atomized powders usually used in AM industries. A physics-based processing diagram was developed based on melting modes to address the primary challenge associated with the 7A76 alloy, namely the achievement of high relative densities. Inductively Coupled Plasma (ICP) Spectroscopy was used to validate final chemical composition. Advanced characterizations including computed X-ray tomography (XCT) and Field Emission scanning electron microscopy (FE-SEM) were utilized for microstructure examination. It was discovered that printing across different melting modes can greatly impact the evaporation of volatile elements such as Zn and Mg. Ultimately, a relative density of 99.98% was achieved, which is the highest relative density reported for this material system.