Mechanism Research Of Resistance Spot Welding Process Between Automotive Steel And Aluminum

With the development of entire auto industry, saving resources and reducing environmental pollution become the two major problems to be solved. As the most important automotive two lightweight types of materials, steel-aluminum integrated framework body structure consisted of high-strength steel and aluminum alloy is the important way to achieve lightweight and high body strength. In the automotive industry, resistance spot welding is the main connection technology. But there are large difference in electrical conductivity, thermal conductivity and other physical properties between steel and aluminum, and it is very easy to form brittle intermetallic compounds between them, making it difficult to form high quality stable spot welding joints. Therefore, it is great value in engineering to carry out the dissimilar materials research of high-strength steel and aluminum resistance spot welding mechanism. In this paper, a preliminary exploration of high-strength steel and aluminum resistance spot welding study was conducted. The recent development of the research on the resistance spot welding of steel- aluminum is introduced in this paper. Based on the environment of software SORPAS, a finite element model for the spot welding process of DP590 dual-phase steel and 6061 aluminum alloy is established. Thermo-physical properties parameters are tested for this simulation, and introduced the formation mechanism of steel and aluminum resistance spot welding joints, described three stages of steel and aluminum welding joints formation and characteristics of melting nuclear. By macro- and micro-metallographic analysis of spot welding joints, found that the nugget of the steel side is offset because of heat production and heat dissipation inequality of two each side of the steel and aluminum during the spot welding process. So the process is melted aluminum alloy in the interface of steel-aluminum spread out on steel, so it nature belongs to melt-brazed joints.In this paper, designed and conducted a series of different welding parameters and mechanical analysis of welding test, By the corresponding mechanical experiments, when the welding current increased from 8.3kA to 9.7kA, the strength of welded joints increased with the increase of welding current. But when the welding current increased over 9.7kA, the heat input was so much that the liquid metal in the aluminum-side nugget got splashed. As a result, the strength of spot welded joints got reduced.In this paper, by the law of DP590 and 6061 aluminum alloy welding parameters on nugget diameter with the servo resistance spot welding machine and AC resistance spot welding, weld nugget diameter increased with the heat input, when the nugget diameter increases to a certain value, the nugget diameter remained stable within a certain range although continuing to increase the welding current. But the nugget organization will overheat, the grain will become coarse and it yielded the splash and the performances of welded joints have an adverse effect. It is basically the same of tensile strength and tensile-shear strength with the current trend between servo resistance spot welding machine and AC resistance spot welding.In this paper, the interface elements of spot welding joints were analyzed and found that the crystal is formed between the steel and aluminum compounds, when the percentage reached 40% of the aluminum atoms during aluminum to steel in the diffusion process. As a result, in this area it did not achieve the compact connections.