Mechanism And Control Method Of Defects In Plasma Arc Welding Of Medium Thickness Plate Of 6061 Aluminum Alloy

In etching,ion implantation,PVD,CVD and other IC equipment,most of the cavity parts are made of medium thickness plate of aluminum alloy by integral milling.If near-net-shaping of aluminum alloy parts is realized by welding technology,it is expected to greatly reduce the processing cost of some cavity parts and provides technical solutions for supersized aluminum alloy parts needed by domestic IC equipment and other semiconductor equipment.Plasma arc welding process has high welding efficiency,good adaptability,stable welding process and high welding quality,so it has a broad application prospect.In IC equipment,cavity vacuum sealing is one of the most important indexes,so weld defect suppression is very important;At present,the research on plasma arc welding of aluminum alloy focuses on the design and development of welding system,numerical simulation and mechanism research,while the research on defect suppression of plasma arc welding of medium thickness plate of aluminum alloy is less.In this paper,7 mm thick 6061-T6 aluminum alloy was used as the research material to carry out the experiment of single-sided welding and double-sided forming of plasma arc welding.The external defects represented by incomplete penetration and internal defects represented by porosity were studied,and the suppression ways were put forward.The main contents and conclusions are as follows:(1)Welding platform were set up.The platform was composed of wire feeding device,energy supply device,welding torch walking device and welding table,which could adjust the main process parameters and ensure the smooth progress of the experiment.(2)Aiming at the external defect of incomplete penetration,the influence of parameters on the surface morphology was studied by single factor experiment.The results showed that:the appropriate arc current,welding torch angle,plasma gas flow rate,cleaning time scale,welding speed,wire feeding speed,and groove size can obtain good surface morphology without external defects.(3)Based on the range of welding parameters with good weld surface morphology,the main internal defects of aluminum alloy during plasma arc welding were studied.It was found that hydrogen porosity is the main defect in the weld.With the change of arc current,welding speed,cleaning time scale and groove angle,the porosity first increased and then decreased;With the change of groove gap,the porosity presented an increasing trend.(4)Based on the optimized parameters,two schemes of preheating before welding and remelting after welding were proposed to further inhibit the generation of porosity.The internal influence mechanism was analyzed and the nondestructive testing was carried out to check whether the weld met the requirements of IC equipment.The results showed that preheating before welding could reduce the porosity by removing the hydrogen content on the surface of the plate and reducing the solidification rate of the molten pool,and the porosity decreased by 18.92% after preheating;Remelting after welding was mainly aimed at the large pores near the weld surface,which made the large pores near the weld surface escape for the second time,so as to inhibit the generation of pores.The porosity decreased by 10.81% after remelting.