Abstract
Effects of weld composition and heat input on microstructures and mechanical properties of tungsten inert gas (TIG) welded magnesium alloy AZ91D joints have been investigated. Increasing magnesium alloy weld Al contents from 6.9 to 9.8 wt%, the area fraction of brittle Al12Mg17 phases in the weld metals increased from 6.2 to 7.3% and the strength and elongation of the weld metals decreased from 215 MPa and 7.9% to 192 MPa and 4.9%. Increasing the heat inputs from 73.6 to 147.2 kJ resulted in the grain coarsening of the weld metals and the partially melted zone (PMZ) width increasing from 120 to 210 μm. The mechanical properties of welded joints are poor compared with those of the base metal AZ91D. The strength and elongation of the joints are about 70% and 73% of the strength (156 MPa) and elongation (4.8%) of the base metal, respectively. The joint fractures mainly occurred in the PMZ with broader Al12Mg17 phases at the grain boundaries.
