Study on microstructure and mechanical properties of Al–Mg–Mn–Er alloy joints welded by TIG and laser beam

Al-4.7Mg-0.7Mn-0.3Er alloy plates were welded by laser beam welding (LBW) and tungsten inert gas (TIG). Mechanical properties and microstructures of both welded joints were analyzed. The results showed that the tensile strength of LBW joint was 315 MPa, which was approximately 10% higher than that of TIG welded joint. This was attributed to the fine grains, dispersed primary Al3Er phase and low Mg evaporation in LBW weld. Equiaxed grains with average size of 30 μm were obtained in the fusion zone, which were much smaller than that of 90 μm in the fusion zone of TIG joint, due to the low heat input during LBW process. Moreover, finer primary Al3Er particles were uniformly distributed in the LBW joints, which resulted in a substantial increase of nucleation rate in LBW welds. In addition, it was also found that Mg concentrations in the fusion zones, in both TIG and LBW joints, were lower than that of the base one tested by EPMA. The burning loss rates of Mg in TIG and LBW joints were 36% and 22%, respectively.

► The microstructural characterization of the TIG and laser welded Al–Mg–Mn–Er alloy is studied.
► Transition zone and HAZ are found to disappear near the fusion boundaries in LBW joint.
► Primary Al3Er in LBW weld provides more nucleation sites and lead to the grain refinement.
► The evaporation of alloying element Mg in TIG and LBW joints is investigated.
► Reasons for high strength of LBW joint are fine-grain strengthening and solution strengthening.