Gas Metal Arc Welding (GMAW) Process Optimization of a 1.4 mm Uncoated Dual Phase 980 (DP980) Joint for Automotive Body Structural Applications

Abstract

With the increasing demand for safety, energy saving and emission reduction, Advanced High Strength Steels (AHSS) have become very attractive steels for automobile makers. The usage of AHSS steels is projected to grow significantly in the next 5–10 years with new safety and fuel economy regulations. These new steels have significant manufacturing challenges, particularly for welding and stamping. Welding of AHSS remains one of the technical challenges in the successful application of AHSS in automobile structures due to heat-affected zone (HAZ) at the weld joint. In this study Gas Metal Arc Welding (GMAW) of a lap joint configuration consisting of 1.4 mm uncoated DP980 to itself was investigated. The objective of the study was to understand the wire feed rate and torch speed influence on lap joint tensile strength (static and fatigue). A two factor, two level, full factorial design of experiment (DOE) was conducted to understand the wire feed and torch speed influence on tensile and fatigue strength of the welded joints. In order to understand the curvature effect, a center point was also included in the experiment. Based on the statistical analysis, neither factor was significant on static tensile strength, however, a two way interaction between wire feed rate and torch speed was significant on static tensile strength. Metallurgical properties of the lap joints were evaluated using optical microscopy. A significant hardness drop of 40% was observed at the HAZ.