Microstructural characteristics and mechanical properties of non-combustive Mg-9Al-Zn-Ca magnesium alloy friction stir welded joints

摘要

Non-combustive Mg-9Al-Zn-Ca magnesium alloy was friction stir welded with rotation speeds ranging from 500 to 1250 rpm at a constant welding speed of 200 mm/min. Defect-free joints were successfully produced at rotation speeds of 750 and 1000 rpm. The as-received hot extruded material consisted of equiaxed α-Mg grains with 3-Mg_(17)Al_(12) and Al_2Ca compounds distributed along the grain boundaries. Friction stir welding produced much refined a-Mg grains accompanied by the dissolution of the eutectic p-Mg_(17)Al_(12) phase, while Al_2Ca phase was dispersed homogeneously into the Mg matrix. An increase in rotation speed increased the a-Mg grain size but not significantly, while microstructure in the heat affected zone was almost not changed compared with the base material. The hardness tests showed uni form distributed and slightly increased harness in the stir zone. Results of transverse tensile tests indi cated that the defect-free joints fractured at the base material, while longitudinal tensile tests showed that the strength of the defect-free welds was improved due to microstructural refinement and uniform distribution of intermetallic compounds.