Study On Interface Control Of TIG Welding-brazing Of Aluminum Alloy To Stainless Steel

Hybrid structures of aluminum alloy and stainless steel have the comprehensive benefits, such as light weight, high strength and corrosion resistance, etc. Their application has a high technical and economical potential in aerospace vehicle, automobile and national defense industry. However, joining of aluminum alloy and stainless steel has great difficulty since brittle intermetallic compounds (IMCs) are formed in the joint. Nowadays, arc welding-brazing with the characteristics of convenient operation and high efficiency offers a great potential for material combinations of aluminum alloy and steel. The key issues to obtain high-quality arc welding-brazing joints are to promote the filler metal wetting and spreading on steel surface and to control the brittle IMC layer growth in the Al-steel interface.On the basis of prophase precoating process development and experiments, the effect of alloying elements on the interface structure was studied detailedly and the control mechanism of alloying elements on the interface layer growth was analyzed. Finally, the overall performance of aluminum alloy and stainless steel joint was improved.This subjiect revealed the growth mechanism of interface layer.The effect of different content of Cu element on the structure of the interface was studied and the growth mechanism of interface layer was revealed.Then the study focused on the microstructure and mechanical properties of the joint when the content of Cu element was 6 wt%.With Al-Cu6 filler metal, the interface layer presents short whisker shape consists of onlyθ-Al13(Fe,Cu)4 phase and the whole layer is in 2-5μm thickness. The interface layer has a high crack resistance, and the tensile strength of the joint reaches 150-170MPa. The control mechanism of Cu elements is that Cu can replace some Fe atoms inθ-Al13Fe4 to inhibit its preferred orientation growth. With Cu content of 6wt%, the joint reaches the best mechanical properties.Then the effect of La,Zr,Ag element on the interface was studied.The effect on interface layer by the addition of La element was very small.Zr elements has a significant thinning effect on the interface layer and the weldt; Small crack appeared in the weld by the addition of Ag.The results showed that: under the Al-Cu-La solder the mechanical properties of of the joint is equal to Al-Cu6;The addition of Zr improved the mechanical properties,;Mechanical performance of Al-Cu-Ag solder was decreased.At last,the interface temperature distribution during TIG welding-brazing process was computed by MARC finite element method. The temperature field simulation results show that the liquid-solid interface temperature is uneven with the gap of nearly 300℃and 2.5s from the top to the bottom of the groove and the peak temperature ranges from 700 to 1200℃and the reaction time is less than 10s with different heat input.Combination of the interface structure at different heat input conditions, found that the interface layer thickness was uniform and the mechanical propertiesof the jiont was best when the peak temperature of the interface at about 1000℃.