Joining of Aluminum Alloy to Steel Using Pulsed-MIG Welding

摘要

Ability to join steels to aluminum alloys enables selective replacement of heavier steel parts with lighter aluminum alloy parts, for light weighting. For example, light weighting of automotive body-in-white structures. However, accomplishing good joint efficiency in fusion welding of such dissimilar material combination is very difficult due to formation of brittle inter-metallic phases in the fusion zone. Recently, there have been research reports that aluminum alloy-steel joints of usable mechanical strength can be achieved by using such welding conditions that minimize intermetallic phases at the interface to less than 10 μm. Low heat input processes are well suited to achieve such minimal intermetallic formation. Pulsed MIG welding is a widely used technique for thin section welding due to possibility of welding at very low mean currents combined with controlled metal transfer. In this work synergic pulsed MIG welding process was used to fusion weld galvannealed steel sheets (1.2 mm thick) to aluminum alloy 6061-T6 sheets (2 mm thick) in lap fillet configuration. The aluminum sheet is placed on the steel sheet and the pulsed arc run along the edge of the aluminum sheet. The objective was to melt the aluminum side and wet the steel side with molten aluminum to form the joint. Experiments in this configuration were conducted using various welding parameters and arc positions. Joints could be made successfully with very thin inter-metallic layers at the aluminum-steel interface in the range of 5-15 μm. Metallurgical features and mechanical properties of these joints at various pulse-MIG welding conditions are reported in this paper.