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With the increasing demand for safety, energy saving and emission reduction, Advanced High Strength Steels (AHSS) have become very attractive materials for automobile makers. Welding of AHSS remains one of the technical challenges in the successful application of AHSS in automobile structures, especially when durability of the welded structures is required. In this study, 2.0 mm uncoated DP780 was investigated. GMAW welding parameters for lap joints of this steel were developed in order to obtain different weld geometries defined by weld toe angle, weld leg sizes, and weld penetration. Metallurgical properties of the joints were evaluated using optical microscopy and scanning electron microscopy (SEM). Static and fatigue tests were conducted on the welded joints. Effect of weld geometry and HAZ softening on fatigue performance including fatigue life, crack initiation site and propagation path of the joints will be analyzed.

Fuel economy and federal safety regulations are driving automotive companies to use Dual Phase and other Advanced High Strength Steels (AHSS) in vehicle body structures. Joining and assembly plays a crucial role in the selection of these steels. Specifications are available for the resistance spot welding (RSW) of lower strength sheet steels, covering many aspects of the welding process from the stabilization procedure to endurance testing. Currently, specifications in the automotive industry for RSW with AHSS are limited. It is well known that welding of a thickness ratio greater than 1:2 poses a challenge. To utilize thinner gauge AHSS panels on body-in-white, welding schedules to join the thin to thick sheet steel stack-up are needed. Most of the existing published work was conducted on uncoated sheets and welded to the same thickness.

The automotive industry is in constant pursuit of alternative materials and processes to address the ever changing needs of their customer and the environment. This paper presents findings from a study using a laser hybrid process (laser with MIG) to join aluminum-silicon coated boron steel (USIBOR). In this report the influence of heat from the laser hybrid welding process and its effect on the coated boron steel is discussed. In order to understand the affect from laser hybrid joining process, bead on plate experiments were conducted using 1.0 mm, 1.6 mm and 2.0 mm thick coupons. Further, two lap joint configurations were also investigated using the 1.6 mm and 2.0 mm thick coupons. Based on the test results, a significant reduction in tensile strength was observed at the Heat Affected Zone (HAZ).

Typical automotive joints are lap, coach, butt and miter joints. In tubular joining applications, a coach joint is common when one tube is joined to another tube without the use of brackets. Various fusion joining processes are popular in joining coach joints. Common fusion joining processes are Gas Metal Arc Welding (GMAW), Laser and Laser Hybrid, and Gas Tungsten arc welding (GTAW). In this study, fusion welded 2.0 mm uncoated DP780 steel coach joints were investigated. Laser, Gas metal arc welding (GMAW), and laser hybrid (Laser + GMAW) welding processes were selected. Metallurgical properties of the DP780 fusion welds were evaluated using optical microscopy. Static and fatigue tests were conducted on these joints for all three joining processes. It was found that joint fit-up, type of welding process, and process parameters, especially travel speed, have significant impact on static and fatigue performance of the coach joints in this study.