Microstructure and Mechanical Properties of Al–Li Alloys with Different Li Contents Prepared by Selective Laser Melting

Abstract

Research on the development of new lightweight Al-Li alloys using a selective laser melting process has great potential for industrial applications. This paper reports on the development of novel aluminum-lithium alloys using selective laser melting technology. Al-Cu-Li-Mg-Ag-Sc-Zr pre-alloyed powders with lithium contents of 1 wt.%, 2 wt.% and 3 wt.%, respectively, were prepared by inert gas atomization. After SLM process optimization, the microstructure and mechanical properties of the as-printed specimens were investigated. The densifications of the three newly developed alloys were 99.51%, 98.96% and 92.01%, respectively. They all had good formability, with the lithium loss rate at about 15%. The as-printed alloy with 1% Li content presented good comprehensive properties, with a yield strength of 413 ± 16 MPa, an ultimate tensile strength of 461 ± 12 MPa, and an elongation of 14 ± 1%. The three alloys exhibited a layered molten pool stacking morphology and had a typical heterostructure. The columnar crystals and equiaxed fine grains were alternately arranged, and most of the precipitated phases were enriched at the grain boundaries. The change in Li content mainly affected the precipitation of the Cu-containing phase. When the Li content was 1 wt.%, the following occured: θ phase, T₁ phase and T_B phase. When Li increased to 2 wt.%, T₁ and T₂ phases precipitated together. When Li reaches 3 wt.%, δ' phase precipitated with T₂ phase. This study provides useful guidance for the future SLM forming of new crack-free and high-strength Al-Li alloys.