Cold metal transfer welding of automotive high strength steel

Abstract

The increasing demand for high-strength steels (HSSs) in the automotive industry has prompted concerns about weldability. The welding of HSSs often leads to cold cracking phenomena due to factors such as high carbon equivalents, hydrogen diffusion, etc. Cold metal transfer (CMT) welding is an innovative alternative to conventional gas metal arc welding (GMAW) and offers advantages such as lower heat input (Q), reduced distortion, and lower spatter. However, optimizing CMT parameters for welding HSS joints remains a challenging task. This research aims to optimize CMT welding parameters for HSS DP1000 steel joints with a thickness of 1 mm, employing two different welding speeds (40 cm/min and 50 cm/min). The mechanical properties (microhardness, tensile test with fractography, and bending test) and the microstructural properties were analyzed and compared. Also, a high-speed camera and synchronous electrical signal acquisition device were used to examine droplet transition characteristics. Microstructures in the base material (BM) comprise martensite and ferrite while with higher heat input, the heat-affected zone (HAZ) has coarser microstructures. Overall microhardness results indicated a reduction in values at a welding speed of 50 cm/min compared to 40 cm/min. Tensile strength results demonstrated the higher strength of the joint with a higher welding speed. Moreover, no cracks were detected in the bending test for joints with both welding speeds. Consequently, it can be concluded that samples welded at a speed of 50 cm/min exhibit enhanced mechanical properties.