Study On CP Arc Welding-brazing Of Aluminum Alloy To Stainless Steel

Hybrid structures of Aluminum alloy/stainless steel offer the potential to utilize the advantages of the two materials, which are suggested in aerospace and transportation for their light weight, high tension and high corrosion-resistance. It is also a great challenge to join these two materials together because of great differences in thermo-physical and mechanical properties, the easily formation of brittle intermetallic compounds which can reduce the mechanical performance of the dissimilar materials joints. Reliable joints can be obtained via solid-phase welding, brazing and some other processes. However, these methods need either strict technological requirements or workpieces with certain shapes. On the contrary, the arc welding-brazing method has special advantage in aluminum/steel joining because of its small amount of heat input, simple operating and easy to achieve auto-control.Considering the welding characteristics of the aluminum/steel dissimilar metals, CP welding machine was chosen to join aluminum alloy to stainless steel using the arc welding-brazing method. In order to promote the wetting and spreading of filler metal on steel surface, galvanizing coating, precoating layer and aluminized coating were carried out before welding. Lap joints and butt joints were made by Workpieces of 1mm and 3mm in thickness, respectively. On the basis of different processing conditions, appearances of the joints with different weld parameters were analyzed, and microstructures of the joints in different areas were discussed, and mechanical behavior of the joints was assessed and the effect of interface structure on the mechanical behavior of the joints was also studied.The results of lap joints of 1mm aluminum alloy to galvanized stainless steel showed that thickness of the compound layer in the interface area had grown from 2μm to about 10μm along with the increase of welding heat input; a Al4.5FeSi phase was formatted in the melting zone near the interface layer; tensile strength of the joint can reach 193.4MPa when heat input was 83.44KJ/m, and the shear strength of the interface layer was between 105MPa and 120MPa; shear strength of the joint was 124MPa when pure Al filler wire was used; hardness of the seam was biggest when Al-Si12 was chosen as the filler metal but still below that of the aluminum base metal. The results of lap joints of 1mm aluminum alloy to precoated stainless steel showed the compound in the interface layer turned into the melting zone after broken due to its brittle along with the increase of the welding heat input; tensile strength of the whole joint got 190MPa when the heat input was 86.9KJ/m; the fracture mode can be divided into the plastic fracture in the weld seam near the heat affected zone in the aluminum side and the brittle fracture through the interface layer. The result of butt joints of 3mm aluminum alloy to precoated stainless steel showed that joints had a sound double-side forming owing to the joint gap and grooving, and the weld seam consisted mainly of -Al and Al-Si eutectic, in which broken or needle-like brittle compounds were not detected; joints fracture through the interface layer under tensile test with a strength reaching 157.8MPa. The results of lap joints of 1mm aluminum alloy to aluminized stainless steel showed that the liquid metal had a bad spread in the steel surface, and there were fragile intermetallic formed in the interface layer and also obvious micro-cracks between the compound layer and the steel side; the joint cracked from the interface area with a poor strength which was about 60MPa.