Analysis Of Welding Joint Microstructure Of Copper Aluminum Casing Extrusion Resistance And Its Property Research

The Casing Extrusion Resistance welding technology studied in this paper is anew technology to solve the brass and aluminum problems. In this paper, opticalmicroscopy and scanning electron microscopy were used to characterize the weldingjoints. Combined with welding process and metal solidification principle, wediscussed the morphology of copper and aluminum tubes welded joints. Furthermore,we tested the peel strength of Cu-Al pipe by the stretching machine to explorewelding technology’s influence on the joint strength. At the same time, the corrosioncondition of welding joint was also studied under neutral salt-fog test. For the copperaluminum brazing welding head are more widely application in the production, wecontrasted the corrosion behavior between extrusion resistance welding joint andbrazed joint to discover the corrosion resisting property of extrusion resistancewelding joint. Research showed that:(1) The weld of copper aluminum joint is flat in this by using this technology.The weld interface has a layer of transition layer with different thickness, which isassociated with the welding process. The transition layer narrow sample own highjoint strength. Transition layer with wider areas such as aluminum and eutecticorganization, so the sample of the joint strength is not high. The aluminum-copperbinary alloy phase diagram shows copper aluminum eutectic organization in thewelding process is inevitable, but a special process of this technology can ensure noeutectic organization in the weld area5mm. In this area, the copper aluminuminterface presents the jagged shape, with columnar crystal morphology, thickness ofabout1to2microns. By SEM and TEM, the interface microstructure of the jointare mainly-Al、Al2Cu、Al4Cu9, etc. The Al2Cu area is near the aluminum side, whileAl4Cu9in the region of the copper side. They are block distribution with a bad effect on weld strength.(2)A large number of specimens for mechanical testing were studied. By the peeltest and microstructure can be seen that: The copper aluminum welding’s peelstrength with core bar are significantly better than those without core bar, and peelstrength of different locations in the same weldment is slightly different. The linescanning of the interface layer of copper aluminum can be concluded: The diffusionof atoms to the aluminum side is far deeper than to the copper side, which push theinitial interface layer to the aluminum side. The columnar crystal in interface is verysmall, and that improves the strength of joint. If the eutectic organization generatedhad small layer spacing, it also can improve the mechanical properties of materials.But too much of eutectic organization will increase the material brittleness. Lowmelting eutectic organization may become a weak zone to result in a decline inperformance.(3)Under the condition of salt fog, Copper and aluminum extrusion resistancewelding joints are corroded and the corrosion of and aluminum matrix is the primaryfactor. The failure of brazed joints is mainly shown as the failure of solder layer. TheAl in the solder layer and the Zinc in grain boundary constitute the primary cell. Thecrack grows along grain boundaries by cavitation. Combined with electrochemicalcurve, from the point of the corrosion, the corrosion resistance of resistance weldingjoint is superior to that of brazed joints.