Porisoty Formation Mechanism And Control Of EBW 1060/2A12 Dissimilar Aluminium Alloy Seam

Porosity defects are one of the most common defects in aluminum alloy electron beam welding process,which limit the application of aluminum alloy structure.Therefore,the research of the mechanism and control of aluminum alloy pore defects is the focus of study on aluminum alloy electron beam welding.In this paper,research on the porosity defects and related mechanism of the electron beam welding of dissimilar aluminum alloys were carried out with 1060 and 2A12 aluminum alloys.To control the porosity of aluminum alloys in electron beam welding,the characteristics of porosity were analyzed,and the influence of welding parameters on the generation of porosity in aluminum alloy was studied.Based on the simulation results,combined with the knowledge of keyhole and pool dynamic behavior during electron beam welding of aluminum alloy,the mechanism and control methods of pore defects during electron beam welding of dissimilar aluminum alloy were discussed.Weld porosity during electron beam welding of dissimilar aluminums could be classified into "Metallurgical feature-type" pores and "process-type" pores.The former were featured by round shape and small size,which nearly had no adverse effect on the mechanical properties of the joint.While the latter were irregular in shape and larger in size,which could reduce the bearing area of the joints and cause stress concentration,thus reducing the mechanical properties and service reliability of the joint.The formation process of the pores included two stages of bubble generation and bubble floating."Metallurgical characteristic" pores were mainly caused by cavitation in the molten pool and the "process-type" pores were related to the unstable opening and closing behavior of the keyhole,which would wrap metal vapor to form large-size bubble after the keyhole collapsed.Porosity defects would generate if bubbles did not escape before the molten metal solidified.Under the test conditions,the porosity defects of the aluminum alloy joint were related to the penetration status,the porosity of the critically penetrated joint was low,and the porosity of the beam joint increased when it was slightly penetrated.When the welding speed changed from 300mm/min to 1200mm/min,the porosity in the critically penetrated joint first increased and then decreased.Based on the actual process of electron beam welding,flow simulation model was established to study the aluminum alloy welding process.The cavitation potential model and gas particle model were introduced,what’s more,the keyhole behavior and the flow behavior of the molten pool were analyzed.The results showed that the metal vapor reaction force was responsible for surface collapse defects and pores defects during 2A12 aluminum alloy electron beam welding.The stability of keyhole was related to the electron beam energy density reaching the inner keyhole,so increasing the electron beam for the fully penetrated joints was advantageous for reducing the porosity defect.Finally,based on the analysis of the mechanism and influencing factors of weld porosity defects,control schemes were proposed.