마찰교반용접을 이용한 알루미늄 합금 Al5052의 TWB 용접 특성에 관한 연구

Abstract

Recently, fuel-efficiency regulations, light-weight and environmental regulations have been strengthening all over the world. Vehicle weight is one of the most realistic alternatives in the automotive industry because it can be expected to gave effects on fuel consumption and exhaust emission reduction as well as performance improvement through weight reduction as a key factor that determines fuel efficiency. Currently, focusing on the development of lightweight automobiles and welding and bonding process technology to cope with this trend. In order to realize automobile weight reduction, materials of body and parts considering economical efficiency are replaced by lightweight materials such as high strength steel, aluminum alloy, magnesium alloy. However, welding process technology applying lightweight materials to automobiles has not yet achieved the optimum method. It is a trend to apply friction stir welding, in order to minimize the deformation of aluminum alloy weld defect, to ensure weldability This study has the purpose to investigate the effect of friction stir welding with different thickness aluminum alloys for TWB. 2.5mm(retreating side) and 1.5mm(advancing side) thickness is used as Al5052 for this study. The welding parameters were Y-axis tilting angle 1°,2°,3°, tool rotation speed 400, 500, 600 rpm, travel speed 48, 60 mm/min. The cross section showed that the pin was not reached to the bottom surface as the tilting degree increased. As the rotation speed increases, the heat input increased therefore thinning effect is occurred, and that the different thickness of workpiece led insufficient plastic flow. When Y-axis tilting angle 0°, 1°, 2°, 3° were compared, the best welding condition is Y-axis tilting angle 1°, rotation speed 400 rpm, travel speed 60 mm/min. As a result of the tensile test, the minimum tensile strength value of 194 MPa, which is 86 % of the aluminum base sheet at Y-axis tilting angle 0°. The maximum tensile strength was 212.3 MPa, which is 95 % of the aluminum base sheet at Y-axis tilting angle 1°. The tensile strength was decreased as the rotation speed was increased and Y-axis tilting angle increases, the tensile strength decreased. Hardness test was distributed in a uniform shape at every conditions, hardness value of the welded joint was low than the base material. The highest hardness was confirmed 60 Hv, which is 88 % of the aluminum base sheet at Y-axis tilting angle 1°. The lowest hardness was 52 Hv at 3°, the average hardness tended to decrease with increasing Y-axis tilting angle.