Effect of Heat Treatment Process on Microstructures and Mechanical Properties of Laser Additive Manufactured Al-Li Alloys

The Al-Li alloy plates are fabricated by the laser additive manufacturing technique and the evolution of precipitation phase and the change of mechanical properties during the heat treatment process of Al-Li alloys are analyzed. The results show that the as-deposited microstructures of Al-Li alloys mainly consist of alpha(Al) matrix and T-B (Al7Cu4Li) phase, and there exists a small amount of copper-rich phase in the grain boundary. After annealing, the T-B phase is more evenly distributed inside the grains, where the copper-rich phase almost disappears and the Al-Cu-Fe impurity phase is rarely present in the grain boundary. After solid solution quenching, the T-B phase is nearly dissolved in the matrix and a small amount of delta' (Al3Li) phase appears. After aging, numerous theta' (Al2Cu) and sigma(Al6Cu6Mg2) are mainly precipitated. After heat treatment, the microhardness and tensile strength of Al-Li alloys are increased by 47.6% and 87.7%, respectively, if compared with those of as-deposited alloys.