Influence of classified pore contents on the dynamic strength of the welded joint in gas metal arc welding with different process variants made of galvanized and uncoated complex-phase (CP) steel

Abstract

Increasing requirements in terms of weight, safety, and economy are leading to the use of high-strength steels in automotive construction. The focus is on advanced high-strength steels (AHSS). In chassis applications, complex-phase (CP) steels are frequently used and usually processed uncoated. But the demand for galvanized sheet steel is rising steadily to meet the increasing corrosion protection requirements of automotive manufacturers. Gas metal arc welding (GMAW) is an established joining technology. A typical joint geometry for welded chassis structures is the lap joint. The zinc coating poses a particular challenge in the welding process, especially for this geometry. As a result of its low boiling point, the zinc coating evaporates during welding and can lead to pores in the weld seam. Dynamic (crash) loads play a special role in the design of safety-relevant components in automotive engineering. The dynamic strength of tensile shear specimens made of hot-dip zinc-coated CP steel with a sheet thickness of t = 2.5 mm is presented in this paper, considering the influencing variables of heat input, specimen geometry, and pore content. The results of high-speed tensile tests with a servo-hydraulic high-speed testing machine for the test velocities 0.00017 m/s, 0.05 m/s, 0.5 m/s, and 5 m/s according to SEP 1231 are presented. In addition, the failure behavior of the shear tensile specimens welded as fillet welds by GMAW is analyzed by digital image correlation (DIC), and the resulting fracture mechanisms are investigated and presented by scanning electron microscope (SEM).