Research On Dissimilar Light Weight Alloy Laser Beam Welding

Dissimilar metal plates laser welding of TC4 Ti alloy to L3 industrial pure Al are researched in this thesis.Welding between TC4 and Al categorize into dissimilar metal welding.But TC4/Al welding have their specific characteristic, such as their melting point and laser absorptivity are different greatly, besides general dissimilar metal welding problem. So we analyze their weldability.Because the difference between Ti alloy and Al's laser absorptivity is great, we adopt lap joint and make use of the great laser absorption of Ti, and put it on the Al plate,increase Al plate temperature by thermal conductivity.with temperature increasing,laser absorptivity of Al is increasing,so welding joint is formed.We adopt 1.5mm Ti alloy plates and 1.0 mm Al plates, and the laser beam characteristic we use is 0.3mm spot diameter, 0 defocusing amount. We carry on several experiments by changing laser power and welding speed, and by tensile testing, microstructure and hardness analysis.We respectively research their surface profile, microstructure , mechanical characteristic and SEM pictures.We evaluate Al content in welding by formula of penetration ratio, and the result show Al content increase with heat input increasing. Combining the picture of SEM and energy spectrum analysis, we know intermetallic composites forming in the welding: fast cooling speed in laser welding, short existing time of molten pool, and Al have no enough time to diffuse to welding above ,because Al plate lay under Ti alloy plate in lap welding. In addition, they mainly rely not on diffusion, but convection in Al/Ti molten pool, and large depth-to-width ratio, tack shape welding; Aluminum plates are located in the narrowest position. The aluminum is difficult to reach to the front of the weld and stays at the bottom because of the large liquid metal flow resistance in the weld pool, so the content of aluminum in the bottom of weld is far more than ten percent and they are eventually coming into being intermetallic compounds.Both hardness analysis and energy spectrum analysis prove the existence of tntermetallic compounds. Tensile testing demonstrates it can get the meet capability joint on the conditions of power 1.2kw, weld speed 1.2m/min and energy input 1.0kJ/cm.Based on pictures of microstructure and SEM, we analyze varied weld flaw and resulting causes, including gas pores, cracks and segregation in the welding.