Tensile and fatigue properties of friction stir AZ31B-H24 magnesium alloy welded joints under the influences of pin geometry and tool rotation rate

Abstract

Friction stir welding (FSW) is an innovative joining technology suitable for manufacture of magnesium welded lightweight structures. This paper presents tensile and fatigue crack growth rate (FCGR) behaviors of friction stir AZ31B-H24 magnesium alloy welded joints produced using two different pins, namely cylindrical and square pins at varying tool rotation rates of 910 rpm, 1500 rpm and 2280 rpm. Experiments conducted in this study included microstructural observations, Vickers microhardness measurements, tensile tests, residual stress measurements and FCGR tests. The results showed that increasing tool rotation rate increased ultimate tensile strength (UTS) of the welded joints and the highest values of UTS were achieved at 2280 rpm giving 229.0 MPa for the cylindrical pin and 200.3 MPa for the square pin. In the middle tension M(T) fatigue specimens, FCGR of FSW joint fabricated using the square pin at 2280 rpm was lower in comparison to the weld produced by the cylindrical pin. Subsequently, in single edge crack tension (SECT) specimens, the higher FCGRs were observed as the crack propagated across heat affected zone (HAZ) followed by the crack growth retardation in the weld nugget zone (WNZ). These fatigue crack growth rate behaviors were likely dictated by the weld microstructure and residual stresses.

Keywords

• FSW
• Magnesium alloy
• Pin geometry
• Strength
• Fatigue crack growth rate