Research On Al Tube Extrusion Resistance Welding Process And The Joint Structure And Its Properties

In the refrigeration products, Aluminum replacing copper as the main material ofrefrigeration product line manufacturing has great economic and social benefits. Butthe aluminum pipe connection issue always restricts the trend. In the thesis,properties of aluminum tube extrusion resistance welding joints are studied, whichtheoretically support the usage of aluminum tube extrusion resistance welding inindustry application. The main content of this paper is as follows:Through welding process design, welding samples which have better appearanceand whose mechanical properties are tested good，are obtained using extrusionresistance welding. The suitable welding procedure is: removing membrane beforewelding, argon gas protection in the welding process, pluging type structure, fixedAluminium tube reaching out electrode around1.5mm. Welding parameters are that:Current,7510A; Welding pressure,1000Pa; Conduction time,0.3s. The weldedjoints under the optimum process conditions are tested mechanical properties,including tensile and bursting test. The results show that, welded sample failureposition are located on base metal, far away from the welded joint, the mechanicalstrength of welded joint meet the requirements of use.The structure and the microstructure of welding joint is studied with SEM andOM, and the formation of weld process is also analysed. Welded joint comprise, heataffected zone of socketed tube, welded zone, heat affected zone of inserted tube,turnup part, internal press-in part. Microstructure observations show that weld can bedivided into two areas, fusion welding area and no fusion welding area. Fusionwelding area locate in hot concentrated place, creating a micro melting bath. Therapid cooling after welding, form the fine equiaxed grain, tissue density withoutdefects such as pores and inclusions. No melting area is similar to the solid phasediffusion bonding, which welding seam is straight and the grain boundary is notcompletely disappear. In addition, the range of heat affected zone is measured. Theinfluence on the socketed tube is about300microns, and heat affected zone360microns for the inserted tube.The corrosion resistance of joints are studied by weight loss test and polarizationcurve. The parent metal and Al-Si brazing sample are also tested. Immersioncorrosion test results show that the extrusion resistance welding sample is similar with the base metal, for pitting and corrosion degree. The corroded Al-Si brazing sampleunder the same conditions, aggravate to the spalling corrosion and the corrosionweight loss rate is greater than the former two. Polarization curve results indicateextrusion resistance welding sample has the same corrosion potential with base metal.The corrosion potential of Al-Si brazing sample is lower than the former two.Corrosion resistance test results show that the corrosion resistance of extrutionresistance welding sample are similar to base metal, and better than brazing sample.