Research On Resistance Spot Welding Process And Mechanical Property Of Al-Si Coated Advanced High Strength Steel

Resistance-spot welding is one of the common welding method for automotive BIW welding, bearing the characteristic of high-current, high efficiency, simple process and high automation. Aluminum-silicon coated steel sheet, with the characteristic of stain abrasive and heat resistance, has come into wide use in the field of thermo-forming. Therefore, it is of vital importance to study the resistance-spot welding process and performance of aluminum-silicon coated steel sheet.This thesis takes advanced high strength aluminum-silicon coated steel sheet USIBOR1500P+ as research object. It analyzes resistance-spot welding process and the process of 1.1+1.6mm steel sheet with different thickness through nugget diameter and maximum shear force, micro structure and mechanical property of its joint. It draws the following conclusion: Good-performance joint can be made with appropriate preheating time and current, like welding current of 9.5KA, welding time of 20 CYC, and electrode pressure of 3000 N. Through the study of 1.1mm aluminum-silicon panel with different coating coverage. It draws the following conclusion: with the increase in coating coverage, the current range of welding process keeps on rising, and its rising rate in the upper limit is faster than that in the lower limit. This thesis also analyzes the distribution of aluminum-silicon coating material on the surface of welding nugget and center by dint of point scanning and line scanning, verifying that aluminum-silicon coating material can restrain welding spatter. This thesis explores the welding current of steel sheet with the thickness of 1.2mm, 1.6mm and 1.8mm respectively to study the application of advanced high strength steel sheet in the scene. With the same process parameters, this thesis formulates the process windows of steel sheet with qualified spot welding current and spatter current, providing guidance for future manufacturing. Meanwhile, this thesis optimizes the welding process of high strength steel sheet 1.1+1.6mm with different thickness, comparing the differences in the process of high strength steel sheet before hot stamping and that of high strength steel sheet after hot stamping.Welding joint is made up of base metal, heat affected zone and welding nugget zone. The microstructure of base metal is ferritic structure and a little pearlitic structure. The microstructure of heat-affected zone is pearlitic structure, ferritic structure and a little bainitic structure. Microstructure of welding nugget zone is low-carbon martensitic structure. Therefore, Along from base material zone to nugget zone, the micro hardness is rapidly increased.This thesis concludes the drawbacks of the process of USIBOR1500P+ resistance-spot welding, proposes the commonly-used process measures to avoid these drawbacks.