마찰교반용접(FSW)을 이용한 순 티타늄 판재의 용접부 특성 대한 연구 = A Study on the Friction Stir Welding Properties of Titanium panels

다국어 초록 (Multilingual Abstract)

Titanium and titanium alloy is widely used in heat exchangers due to its unique character of corrosion resistance from the sea water and big in specific strength. Especially the pure titanium is optimum to make heat exchange panels, as pure titanium is good for mold-ability. However there is a potential risk of a flaw in welding when using titanium, due to its strong chemical attraction with oxygen, nitrogen and hydrogen and the characteristic of welded part which is weaker and lighter compared to the deposited metal zone and the parent metal. As a consequence, instead of typical connection methods of fusion welding such as MIG (metal inert gas), TIG (tungsten inert gas) welding, GMAW(gas metal arc welding), laser welding or electron beam welding, the friction stir welding is perceived as more eco friendly, and economic connection method since it is unnecessary to use additional heat source, welding rod and filler metal, as well as there is no spatter, harmful ray or material while connecting. Friction stir welding is when materials near the tool area becomes soften by the friction heat occurred from the friction between the tool and binder, while the materials on the sides of the composite plane are forced to blend by the plastic deformation and flow from the rotary motion of the tool, and the binder joints after cool down. There are 4 major types of titanium – pure titanium, α alloy, α+β alloy and β alloy. Pure titanium Grade 2, one of the most popularly used types of titanium also has been used in this study. Angle butt joint and lap joint of 2mm thick pure titanium panels will be executed using friction stir welding, and then a macroscopic observation will be undertaken about each welding method’s micro Vickers hardness test, maximum load resistance test, the ultimate strength, stress-strain diagram, of the welded part using the produced specimen. The examination results of the tension test, hardness test and modified structure after the execution of butt joint and lap joint friction stir welding using the pure titanium panels are as follow: ⑴ The result demonstrated that the tension and hardness under lap joint welding measured lower than butt joint welding, as the tension force decreased due to the welded part highly affected by the friction heat which lead to weaken of it. ⑵ Having checked on the fractured part after the tension test, butt joint welding method showed typical dimple type refined structure due to ductile fracture while lap joint welding method showed cleavage type microstructural feature due to brittle fracture. ⑶Having observed on the microscopic organization after friction stir welding, it has been revealed that it transforms into a different structure from the parent metal. The structure on the stir zone becomes more fineness structural than the parent metal, and such incident happened more on the lap joint welding which has a higher revolution speed of welding roll. ⑷ When executing friction stir welding using 2mm thick pure titanium panel, butt joint welding seems to be more ideal than lap joint welding in terms of mechanical characterization and microstructural characterization.

목차 (Table of Contents)

• Ⅰ. 서 론
• Ⅱ. 실험 방법 및 조건
• Ⅲ. 실험 결과 및 고찰
• Ⅳ. 결 론