Process Analysis Of Heterogeneous Aluminum Alloy Welding Of HX3 Locomotive Door

Locomotive door is one of the most important components for the carbody structure, a key subassembly to the safe operation of the locomotive and even an escape means of driver and passengers in case of emergency, therefore the requirements for the manufacture and inspection of locomotive door are very strict in railway industry. In this paper, according to the structure characteristics of the locomotive door, test samples are made of two types of aluminum alloy in the HX3 locomotive door application under different welding process parameters. Research of metallurgical structure, mechanical property and defect state are conducted for weld joints under various welding process. The comprehensive performance, transformation mechanism and defects of the welded joint are analyzed based on mechanical properties, chemical composition and macroscopic and microscopic examinations which are conducted by metallographic microscope, scanning electron microscope and X-ray diffraction test. A direct relationship between the welding seam micro structure and its corresponding performance is drawn.It is found through contrastive observation of welding seam micro structure between different groups of samples that, during welding with ER4043 and ER5356 filler material, the change of the grain size is not significant for the area close to the heat affected zone of the parent material 6063. The grain size is the same as the weld seam grains. However, relatively bulky equiaxed grain appeared in the heat affected zone close to the die-casted aluminium, which is the weak region of the sample. Samples welded with low current parameter yield finer grain structure and result in a best tensile strength, and Mg2Si strengthening phase which is homogeneously distributed in the matrix is mainly granulate and coralline morphology near both sides of the welding line. Such distribution of Mg2Si strengthening phase in the welded joint ensures stable mechanics performance of the welded joint. Under the same welding parameters, the bending angle of the sample welded by ER4043 filler material is smaller than that welded by ER5356 filler material, which illustrates that the toughness and plasticity of the welding seam by ER4043 is higher than that by ER5356. It is finally verified that the best welding process of the locomotive door, under which the comprehensive mechanics performance of the welding line and heat affected zone is best, is to weld by ER4043 filler material with the welding current of 70-80A at a wire feed rate of 4.3mm/s.