Microstructure evolution and mechanical behavior of Al–Li alloy fabricated by laser melting deposition technique

This paper systematically studies the microstructure evolution, tensile property and microhardness of Aluminum-lithium (Al–Li) alloy with dimension of 80 mm × 30 mm × 80 mm manufactured by laser melting deposition (LMD) technology. Results indicate that the microstructures of the as-deposited Al–Li alloy are variable from the top to the bottom of the plate. At the top region, a fully dendritic structure is observed with underdeveloped secondary arms. And the copper-rich precipitates with irregular stripe morphology appear in the inter-dendritic areas. Attributing to the thermal cycle during laser deposition process, as distance increasing away from the top, the number of irregular stripe phases reduces with the massive precipitation of needle-like TB phases (soft and brittle). At the bottom of the plate, dendritics of as-deposited Al–Li alloy obviously coarsened, TB phases fully decorate the entire grains with a few residual copper-rich precipitates. Attributing to the different microstructures, the micro-hardness firstly increases from 121 HV to 134 HV at a distance of 30 mm, and then decreases to about 98 HV at the bottom of the deposited Al–Li alloy plate. The ultimate tensile strength of the as-deposited Al–Li alloy (longitudinal direction, at the middle-bottom part of the plate) is comparable to the hot-rolled Al–Li alloy (244 MPa). However, the yield strength and elongation of the as-deposited Al–Li alloy are relatively poor due to the embrittlement of copper-rich phases as well as TB phase.