자동차 경량화용 마그네슘 합금(AZ31)의 마찰접합 특성에 관한 연구

Abstract

Abstract

Friction welded joint is a solid-state welding process that produces a weld under compressive force of workpieces rotating or moving relative to one another to produce heat and plastically displace material from the faying surfaces. The friction welding has been shown to have significant economic and technical advantages. Recently, according to industrial development, friction welding has been applied on various industries such as automotive component, aerospace, ship, farm machines and machine component fields, etc. However, one of the major concerns in using the friction welding products is the reliability of the weld quality. Reliable nondestructive test evaluation is available at present to check the weld quality, particularly in a production environment. In this paper, friction welded joint was performed to investigate mechanical properties of welded Mg alloy(AZ31) with 20mm diameter solid bar. The main friction welding parameters were selected to endure reliable quality welds on the basis of visual examination, tensile tests, impact energy test, Vickers hardness survey of the bond of area and heat affected zone(HAZ) and macrostructure investigations. And then, the nondestructive technique to evaluate the weld quality was carried out the total counts by acoustic emission(AE) system. The study has led to the following concluding remarks. The tensile strength of the friction welded materials(271MPa) was increased up to about 100％ of the AZ31 base metal(274MPa) under the condition of the heating time at 1sec. The metal loss increases lineally with increasing the heating time. Optimal friction welding conditions were determined as follows; rotating speed(n)=2000rpm, heating pressure(HP)=35MPa, upsetting pressure(UP)=70MPa, heating time(HT)=1sec, upsetting time(UT)=5sec, when the metal loss(Mo) is 10.2mm. Hardness distribution of base metal(BM) shows HV55. All BM parts shows about similar level hardness than friction welded materials. The weld interface of friction welded parts was strongly mixed to show a well-combined structure of macro-particles without particle growth or any defects.