Effect of process parameters on mechanical properties of friction stir spot welded magnesium to aluminum alloys

• Published in: Materials in engineering 2015-02, Vol.66 (PA), p.235-245
• Main Authors: Rao, H.M., Yuan, W., Badarinarayan, H.
• Format: Article
• Language: English
• Subjects: Al alloy; Alloys; Aluminum base alloys; Dissimilar alloys; Failure; Friction stir spot welding; Intermetallic compounds; Lap-shear strength; Magnesium; Magnesium base alloys; Mg alloy; Shoulders; Welded joints
• ISSN: 0261-3069
• DOI: 10.1016/j.matdes.2014.10.065

•Lap-shear failure load of ∼2.5kN was achieved in dissimilar Mg to Al spot welds.•Failure load depends on both welding geometrical features and IMCs formation.•Thin and discontinuous IMCs formed in stir zone are beneficial for weld strength.•Low heat input and good material mixing/interlocking is essential for high strength. Friction stir spot welding was applied to dissimilar cast magnesium (Mg) alloy AM60B and wrought aluminum (Al) alloy 6022-T4 under various welding conditions. The influence of tool rotation rate and shoulder plunge depth on lap-shear failure load was examined. Welds were made at four different tool rotation rates of 1000, 1500, 2000 and 2500 revolution per minute (rpm) and various tool shoulder plunge depths from 0mm to 0.9mm. The cross section of each weld exhibited the formation of intermetallic compounds (IMCs) in the stir zone. An increase in tool rotation rate decreased the width of the stir zone and resulted in lower lap-shear failure loads. The stir zone width increased and interlocking of IMCs was observed with an increase in tool shoulder plunge depth at 1000rpm. High lap-shear failure loads were achieved in welds having a large stir zone width with formation of discontinuous IMCs at the tip of the interfacial hook. An average lap-shear failure load of 2.5kN was achieved for welds made at 1000rpm and 0.9mm shoulder plunge. The present study suggests that the mechanical properties of friction stir spot welded dissimilar alloys are greatly influenced by the stir zone width, interfacial hooks and IMCs which are all weld process dependent.