Effects of preheat treatment on microstructure evolution and properties of brazed-fusion welded joint of aluminum alloy to steel

摘要

Microstructure and mechanical properties of brazed-fusion welded joint of aluminum alloy to galvanized steel were studied by analyzing and comparing the as-welded state and that with preheat treatment at different temperatures. The preheat treatment process not only increased the spreadability of weld seam and thickness of in-termetallic compound (IMC) layer at brazed interface but also changed phase composition of IMC layer. In as-welded joint, there were two IMC layers (layer I included θ-Fe_4Al_(13) and T_5-Al_8Fe_2Si adjacent to weld seam, and layer Ⅱ was composed of η-Fe_2Al_5 near the steel side), while a newly formed nanoscale Fe-rich layer Ⅲ which might consist of FeAl and Fe_3Al was found in the joint with preheat treatment, causing by interdiffusion between layer Ⅱ and Fe at high temperature. Incomplete brazing at weld root deteriorated the strength of as-welded joint The joint with preheat treatment at 100 ℃ fractured at heat-affected zone on aluminum alloy side, exhibited the highest strength which reached nearly 80% of that of aluminum alloy. The thicker IMC layer at weld root led to the fracture at brazed interface when preheat treatment at 200 ℃.