Effect of Al-Si coating weights on weldability of hot-stamped ultra-high-strength steel (UsiborR 1500) used in automotive structures

Abstract

ABSTRACT Automotive industries have seen increased demands for indirect hot-stamped pre-coated ultra-high-strength steel 22MnB5 due to its excellence. This paper presents the results of experimental investigation of the effect of Al-Si coating weights AS150 (150 g/m2) and AS80(80 g/m2) and spot-welding process parameters of indirect hot-stamped Usibor 1500 to further understand which coating weight perform better for automotive application. The resistance spot welding experiments were conducted with a medium-frequency direct control (MFDC) machine. The MFDC resistance spot-welding machine had two G20 electrodes with a 458 truncated cone designed with a diameter of 4.9 mm. The results show that the nugget diameter increases with increasing weld current, better spot-weld nugget diameter is recorded at weld currents above 7.5 kA for both AS80 and AS150 coating weights, and the weld current range decreases with increase in coating weight and with increase in the interdiffusion layer. Heat treatment dwell time has a remarkable influence on weld current range for both AS150 and AS80 coating weights. AS80 coating weight has a slightly higher weld current range of 2.1 KA than AS150 coating weight with weld current range of 1.8 KA. Tensile shear strength for AS150 and AS80 increases nonlinearly with increase in weld diameter.