| With the development of the automotive industry, energy conservation and environmental protection have become an important goal, and lightweight is one of the main ways to achieve this goal. As the most common light metal, aluminum is becoming more and more wildly applied in the field of automobile. Therefore, it is inevitable for the connection of aluminum and steel, and it is very important study on its weldability.CMT spot lap welding of A16061and bare steel or galvanized steel were carried out by using AlSi5filler metal, respectively. Configuration sequence, punching and coating on the properties of the joints were studied and the satisfied joint can be obtained. Using orthogonal test method to optimize process parameters, the microstructures and mechanical properties of welding joint were further studied.The results indicated that:for the joint of aluminum to bare steel sheet, when the aluminum sheet was placed on the bare steel sheet, the weld appearance and mechanical properties of the joint were very poor whether aluminum sheet was punched a hole or not. When bare steel sheet without a hole was placed on the aluminum sheet, the weld appearance and mechanical properties were poor. If bare steel was punched a hole, and weld appearance is good and mechanical properties are stable. For the joining of aluminum and galvanized steel, when the aluminum plate was placed on the top of galvanized steel, the weld joint is acceptable, but the mechanical properties is unstable. Both of the weld appearance and mechanical performance were poor when galvanized steel without a hole was on the top of the aluminum sheet. But if galvanized steel sheet with a hole was placed on the aluminum sheet, the weld appearance was not stable and the mechanical performance was related to the weld appearance. When the weld appearance was good, the mechanical performance was also good and reliable, vice verse. In conclusion, considering weld appearance and mechanical properties, joint of bare steel with a hole on the top of the aluminum sheetwas best mode for joining of aluminum to bare steel by CMT method.The process parameters were optimized by orthogonal test method, and the microstructures and mechanical properties of welding joint were studied. The results show that the satisfied weld appearance and performance can be obtained between A16061and bare steel sheets. The significant sequence of process parameters on mechanical properties has been determined, and the rank is listed, the size of the hole on bare steel sheet, spot welding time, wire feed speed. Typical spot welding-brazing joint can be observed in this study, which is composed of the brazing zone and the welding zone. The joint has a tensile shear load more than4KN and is dominated by tearing fracture.Comparing weld appearance and interfacial microstructure of aluminum-bare steel and aluminum-galvanized steel joints, the burning loss on the back side of the bare steel was more serious and the thickness of interface intermetallic compound was thicker than the size of galvanized steel sheet duo to the evaporation of zinc which can take off some of heat and decrease the temperature of interface. When steel sheet was placed on the top of aluminum sheet, weld appearance was unstable for galvanized steel-aluminum joint. It did not occur in bare steel-aluminum joint. It is because the zinc vapor affected the stability of the arc and led to the instability of the weld appearance. Though the surface method, zinc of galvanized steel sheet in arc area had evaporated at the instant of the arc. Though the cross section method, with the extension of spot welding time, zinc will be gathered in one side to form the rich zinc angle, which was the result of the local spreading out of molten droplet in the action of zinc. The size of the contact angle mainly related to gravity and had little connection with zinc. When the gravity of drop increased with the extension of spot welding tine, the contact angle decreased. In addition, zinc easily gathered in defects such as pore. |
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