Study On High-speed Train Body Of CMT Welded Aluminum Alloy

The 7N01 and 6N01aluminum alloy were widely used in high-speed train body in China and the primang welding method in actual production is P-MIG. Reducing the welding heat input of CMT welding can reduce the ratio of thermal cracking and relieve joint softening, which is important in improving the quality of welding aluminum alloy. A series of bead welding and butt welding used in test, then a compare were made with P-MIG in this paper studying on CMT welding in the aluminum alloy body in used of CMT welding which is a typical low heat input welding techniques.In surfacing experiment of the same line energy, four different operating modes of CMT(including DC CMT, AC CMT, DC CMT mixed with P-MIG, AC CMT mixed with P-MIG) and P-MIG were compared in droplet transfer, characteristics of arc shape, temperature field, microstructure and hardness distribution. Test results showed that arc climbing lead to wire melting efficiency increase, and the dropler transfer of P-MIG in heat input is higher than the CMT’s, so as the proportion of pulse increased in the mixed welding leading to increase the heat input to the base material and the weld fusion ratio.For the 4mm thick 6N01 and 7N01 aluminum alloy,a series of butt welding experiments with mechanical properties testing and microstructure analysis were made. 3 different forms of groove(V-type and Y-type left gap, V-type) were used in this paper in the comparative testes between DC CMT and P-MIG. It was found that welding heat input is the smallest one in use of CMT of V-type left gap and the comprehensive mechanics performance is better than P-MIG welding joints. Using DC CMT welding, the tensile strength of 6N01 aluminum alloy can achieve more than 90% of base material and 7N01 aluminum alloy above 290 MPa, and the bend and impact toughness of DC CMT were better than P-MIG. Analysed microstructure, DC CMT compared with P-MIG the grain refined and the heat affected zone reduced.