통계적 분석에 의한 이종마찰교반용접된 마그네슘 합금의 특성 및 강도 평가

Abstract

Science and technology rapidly develops along with the current of the times. Accordingly, various methods are developed, which enable the weight reduction of products for the reduction of energy consumption together with environmental problems by the weight reduction of machine parts, diverse equipment and so on. Weight is reduced by various types of joining and assembly. However, defects in structural volume, assemblability and the like occur. Accordingly, many products finished in the type of unit with detailed strength are developed. As a result, various welding technologies come into existence. And an effort is made to develop products satisfying weight reduction and structural strength and condition requirements by utilizing a part and various machine materials. The static strength of general welding joint depends on weld metal, part that is directly exposed to heat (heat affected zone), the mechanical properties of material, and besides, force direction, stress concentration, stress type and characteristics, and welding joint type, shape and dimension. Moreover, welding defects are classified into structural defects and dimensional defects. And structural defects include porosity, lock of penetration, slag inclusion, under cut, lack of fusion, and crack, and so on. An effect that these defects have on weld strength is highly dependent on the type. For this reason, using friction stir welding (FSW), solid state joining that welds materials through back-formation flow inside materials by using frictional heat has characteristics of less formation of blow hole or crack and less deformation due to welding than that of fusion welding such as arc, electron beam and laser welding. Together whit this, it is intended to apply a magnesium alloy excellent in strength and weight reduction among machine materials. This has strength, corrosion resistance, toughness, and low-temperature properties. So, many magnesium alloys are used various industries. And its scope of use increases as time goes on. Magnesium having relatively low melting point [651℃] is relatively chemically stable, and is vulnerable to corrosion especially in coastal air. Magnesium alloys have properties excellent in density, thermal conductivity, conductance, specific heat, vibration damping, impact deformation, recycling, etc. On the other hand, when contacting other metal, magnesium alloys corrode earlier. So, it is necessary to be careful in contacting different kinds of metals. Many machine parts using a magnesium alloy as main material are manufactured mostly by welding. Knowledge of fatigue behavior with regard to welding material is very important. There are numerous data on the fatigue behavior of magnesium. However, the condition is that studies on friction stir welding have made relatively very poor progress. The scope of applying the friction stir welding to industries is infinite. And friction stir welding will settle down as core technology in manufacturing process.