Weld fatigue behavior of gas metal arc welded steel sheets based on porosity and gap size

Abstract

Galvannealed (GA) steel sheet is applied to the chassis parts of automobiles with fatigue durability important through gas metal arc welding (GMAW). However, the pores due to zinc vaporization and gaps of the weld deteriorate their fatigue performance. In this study, the tensile shear strength and fatigue behavior of the welds were evaluated considering the porosity and gap size. A GA 590 MPa grade steel sheet with a thickness of 2.3 mm was considered as the base material. GMAW was performed under cold metal transfer (CMT) same welding conditions with a wire feed and welding speed of 7.0 m/min (220 A/16.7 V) and 60 cm/min, respectively, in lap fillet joints with gaps of 0, 0.2, 0.5, and 1.0 mm. The weld porosity was investigated through radiography tests (RT). The tensile shear strength and fatigue properties of the weld were evaluated. For the weld sample without a gap, porosity of 1.4, 4.0, and 6.4 % was detected in the tensile shear specimens through RT, and the tensile shear strength of the weld at RT was reduced 613, 565, and 345 MPa, respectively. For the weld with a gap of 0.2 mm or more, pores were not observed, and their tensile shear strength was maintained at 610 MPa or more. The welds with gaps of 0 and 0.2 mm had a fatigue strength of 91 MPa, whereas those with gaps of 0.5 and 1.0 mm had 62 and 47 MPa, respectively. Thus, the fatigue strength decreased as the gap size in the weld joint increased.