Effect Of Spalling Intermetallic Compounds On The Properties Of Fusion-brazed Joints Between Aluminum Alloy And Steel

The governments around the world have paid serious attention to energy efficient, due to the growing of air pollution and global warming problems. Reducing self-weight of transportation can decrease fossil energy cost and increase energy efficiency. Nonferrous metals such as aluminum alloy have higher specific strength and better corrosion resistance than the ferrous metals. Aluminum alloy has been widely used in automobile, aviation and aerospace industries. But the large differences between aluminum and steel in thermal-physical properties and the formation of brittle intermetallic compounds bring a challenge to the welding of these two materials. Arc-brazing method is a promising way to join aluminum alloy to steel, but the spalling behavior of intermetallic compounds is inevitable.In this paper, filler wires were deposited onto different types of steel, and the lap-joints between aluminum alloy and steel were made by arc-brazing process. The influence of filler wire, element and microstructure of base metal, heat input and arc force on the spalling behavior of Fe-Al-Zn and Fe-Al-Si intermetallic compounds was investigated. The effect of these intermetallic compounds on the properties of lap-joints and the methods restraining the spalling of intermetallic compounds were investigated as well. The results are as follows:The results indicate that Cr could effectively restrain the spalling of Fe-Al-Zn intermetallic compounds and the growing of interfacial layer. The interfacial layer containing Cr element only bulged at some places, and the spalling distance of intermetallic compounds was less than 60?m. However, Cr couldn't restrain the spalling of Fe-Al-Si intermetallic compounds. The shape of intermetallic compounds containing Cr element changed to block-like instead of branch-like.The dissimilar metal joining of 5052 aluminum alloy/ST16 low carbon steel and 5052 aluminum alloy/304 stainless steel were conducted by TIG arc-brazing process. The reduction of heat input could completely restrain the spalling of Fe-Al-Zn intermetallic compounds and the thickness of interfacial layer decreased from 20?m to 14?.m. The morphology of spalling intermetallic compounds layer was that small Fe-Al-Zn intermetallic compounds integrated with Zn-Al solid solution turning into a layer, which could strengthen the weld. However, the reduction of heat input couldn't restrain the spalling of Fe-Al-Si intermetallic compounds. Besides, the needle-like Fe-Al-Si intermetallic compounds had negative effect on the mechanical properties of the joints. The spalling behavior of intermetallic compounds was easy to occur when the joints between aluminum alloy and low carbon steel were made with Zn-15%Al filler wire, but the tensile shear strength was 12-63% higher than using Al-12%Si filler wire. The residual stress of joints between aluminum alloy and stainless steel using Zn-15%Al filler wire was higher than that using Al-12%Si filler wire. It was easy to generate cracks perpendicular to the weld. The tensile shear strength of joints between aluminum alloy and stainless steel using Zn-15%Al filler wire was 6-10% lower than using Al-12%Si filler wire.The joints between aluminum alloy and galvanized steel were made with TIG and CMT process, respectively. The zinc coating could cause the spalling of Fe-Al-Zn intermetallic compounds in the delta region of the joint with a large heat input. The tensile shear strength was not influenced by spalling intermetallic compounds. In the welding process, the arc shouldn't entirely or partially point to the steel. The arc force could facilitate Fe and Cr diffusing to the weld and promote the formation of Fe-Al-Si intermetallic compounds. The zinc coating could prevent arc force from acting on the steel directly. The amount of intermetallic compounds was less than using the steel without zinc coating.