Study On The Al/Cu Welding-brazing Process And Its Interfacial Mechanism

In this paper,a double-electrode micro-plasma arc welding（DE-MPAW）method was proposed.T he DE-MPAW is a suitable method for Al/Cu dissimilar metals welding.The heat input during the Al/Cu welding process can be precisely controlled by adjusting the current parameters of the main circuit and t he bypass.Stable arc and heat input is the key to achieve Al/Cu brazing.Compared with common brazing and other welding methods,DE-MPAW has outstanding advantages such as higher weld quality and on-site operability.According to the basic principle of DE-MPAW,a DE-MPAW system was established.Using a DE-MPAW test platform for flat plate surfacing tests.The results show that,after the addition of co-solvent,the weld spreads evenly and the formation is good,and the best welding parameters of Al/Cu are de termined.T hrough the SEM and EDS observations,it can be seen that from the Cu side to the Al side,the Cu content decreased continuously,and the Al content increased continuously.The Cu Al,Cu₉Al₄ and Cu Al₂ intermetallic compounds was generated on the interface,and accompanied the enrichment with Si elements,showing a black block shape.T he intermetallic compound phase is still distributed from the interface to the weld seam.The white network structure is Cu Al ₂ phase andα-Al eutectic structure;the equiaxed crystal structure isα-Al phase.Annealing tests are performed on Al/Cu welded joints to reduce or inhibit the formation of intermetallic compounds.T he microstructure and mechanical properties of the joints at different annealing temperatures and times were investigated.T he results show,at different annealing temperatures,the maximum intermetallic layer thickness is 36.68μm at 400oC×3h;at different annealing time,the thickest intermetallic compound layer is at 400oC×6h annealing time,reaching 73.29μm.T he interface mainly forms Cu Al₂,Cu Al,Cu₉Al₄,and Cu ₃Al₂.The maximum microhardness at the interface of the joint at 300°C×3h is 435.8HV,and because the intermetallic compound with high hardness is genera ted at the interface,resulting in a higher hardness at the interface than that of the base metal.Appropriate elements in Al/Cu dissimilar metal welded joints can improve the weld properties of joints and affect the mechanical properties of joints.T he ef fects of pure elemental powders Zr,Al and Cu as additive elements on the interface microstructure and mechanical properties of Al/Cu lap joints were studied.A thicker intermetallic compound layer forms at the interface,and Cu Al ₂,Cu Al,and Cu₃Al₂intermetallic compound phases are generated from the Cu side to the weld seam.However,defects such as pores and cracks formed in joints can seriously affect the mechanical properties of joints.Therefore,it is necessary to continue to optimize welding process parameters and obtain well-formed welds.XRD patterns analy ze that Cu₃Al₂,Cu₉Al₄,Cu Al,Cu Al₂,Cu₄Al,Cu₃Al,Al₃Zr intermetallic compounds and Cu_0.5Al_2.5Zr ternary phases were formed in Al/Cu lap joints.Under the same welding process,the maximum load of welded joints with Zr elements is 0.69 k N.Welded joints are fractured at the welds.T he fracture surface is"river-shaped"and belongs to the brittle fracture mode.Aiming at the problem of intermetallic compound growth,the Monte Carlo（MC）method was improved to clarify the interface Al/Cu atom diffusion mechanism.Combined with Cellular Automaton（CA）and MC method,the thermodynamics and kinetics model of intermetallic compound growth in the interface of Al/Cu melt brazing process was established.T h e intermetallic compound growth was simulated.Compared with the intermetallic compounds formed during the actual Al/Cu welding process,it was found that this growth model can simulate the intermetallic compound growth process of the Al/Cu melt brazing interface.It is determined that the concentration and energy have a certain influence on the distribution of the morphology of the intermetallic compounds.