Sang-Woo Song

The Effect of Welding Condition on Tensile Properties of Friction Stir Welds of KS5J32 Al Alloy

The effect of welding condition on tensile properties of KS5J32 Al Alloy was investigated under various welding conditions. The 1.6 mm thick KS5J32 alloy sheets were joined by friction stir welding (FSW) technique with butt joint. The tool rotation speeds were 1000, 1250 and 1500 rpm, and the welding speeds were varied within the range from 100 to 600 mm/min. Voids mainly occurred at the advancing side of the tool probe, when the tool rotation speed was low, due to insufficient materials flow. When the weld pitch exceeded 0.4 mm/rev, voids were observed under all welding conditions and the area of voids increased with increasing weld pitch. For void-free specimens, fracture always occurred at base materials. However voids affected the location of fractures, base metal or welded zone, when the voids existed within the welds.

Effects of titanium on ferrite continuous cooling transformation curves of high-thickness Cr-Mo steels

The effect of Ti on the ferrite-phase transformation in the middle portion of high-thickness Cr-Mo steel vessels was studied. The phase diagrams and ferrite continuous cooling transformation (CCT) curves were calculated thermodynamically, and dilatometry tests were performed to determine the start and finish times of the ferrite transformation. When the Ti concentration was 0.015 mass%, Δ(Fs-Ff) of ferrite CCT curve decreased owing to an increase in the concentration of Mn dissolved as a result of (Mn, Ti) oxide formation. When the Ti concentration was 0.03 mass% or greater, the ferrite CCT curves shifted considerably to the right along the time axis owing to an increase in Ti oxide formation and the precipitation of Ti4C2S2, both of which affect the concentration of Mn dissolved in the austenite matrix. As a result, a completely bainitic structure was obtained when the Ti concentration was 0.03 mass% or greater.

The effects of Welding Conditions on Tensile Properties of Friction Stir Lap Welded of Dissimilar Al Alloy, A6K31/A5J32

The scope of this investigation is to evaluate the effect of joining parameters on the microstructural features and mechanical properties of dissimilar aluminum alloys, 1mm-thickness fixing AA6K31 at the top position and fixing AA5J32 at the bottom position. The friction stir lap welds were studied under various welding conditions, rotation speed of 1000, 1250, 1500rpm and welding speed of 100, 300, 500, 700mm/min, respectively. Mechanical test has been investigated in terms of tensile shear test and hardness test. The results showed that three type nugget shapes such as onion ring, zigzag type, hooking with the void, have been observed with revolutionary pitch. All welding conditions fractured at the HAZ of top plate, A6K31 and also the strength compare with base metal of lap joints were low efficiency, 52~63%. The thickness of fractured position was decreased with the lower heat input conditions. The relationships were excellent due to linear between the effective thickness of fractured position and peak load. The fractured position was the interface between joint area and not joint area. Also the strength efficiency compared with base metal was lower than decreasing rate of thickness because the hardness was decreased at fractured position due to softened material.

Liquation Cracking of Mg and Al Alloys during Friction Stir Welding

마찰교반접합(friction stir welding, FSW)은 고상(solid state)에서 이루어지는 공정으로서 기존 용융용접법으로는 접합이 매우 어렵거나 불가능한 것으로 여겨져 왔던 재료 간의 접합에 새로운 가능성을 제시하고 있다. 마찰교반접합은 비금속인 폴리머부터 고융점의 티타늄 합금에 이르기까지 다양한 재료에 적용할 수 있으나, 개발 초기부터 현재까지는 알루미늄 합금과 같은 저융점 재료를 중심으로 적용되어 자동차, 항공기, 철도차량, 선박, 로켓연료탱크와 같은 수송 분야에 상업화되어 사용되고 있다. 특히 자동차 산업 분야에서는 차체경량화를 위하여 경금속인 알루미늄과 마그네슘 합금의 수요가 증가되었고, 이에 따라 엔진, 열교환기, 휠, 서스펜션 암, 범퍼빔, 차체 등에 적용되고 있다. 최근에는 철강, 니켈 합금, 티타늄 합금과 같은 고융점 재료 및 이종 금속 간의 접합에 대한 연구과 활발히 진행되고 있으며 그 적용이 점차 확대되고 있다

Microstructure and Mechanical Properties of 9Cr1Mo Steel-12Cr2Si Steel Bimetallic Billet Produced by Centrifugal Casting

Lead cooled fast reactor (LFR) is one of the next generation of nuclear plants. Tubes in LFR coolant system requires high temperature strength and Lead-Bismuth eutectic (LBE) corrosion resistance and. 9Cr1Mo steel - 12Cr2Si steel bimetallic billet that satisfies above properties has been produced by dual centrifugal casting. Bimetallic billet was normalized for 1 hour at 1050°C and air cooled. After normalizing, tempering was performed for 1 hour at 750°C and air cooled. Mechanical properties of 9Cr1Mo material satisfied ASME Code Section II Part A SA-426 CP91 standard. 9Cr1Mo steel has tempered martensite structure and 12Cr2Si steel has tempered martensite-ferrite mixed structure. The width of mixed zone was about 1000μm. The LBE corrosion resistance was indirectly verified by observation of oxide layer. After heat treatment, hardness of 9Cr1Mo steel was about 240Hv and 12Cr2Si steel was about 200Hv. As a result of high temperature tensile test, the suitable hot work temperature range was 1000°C and 1100°C. Thermo-Calc calculation result shows that the austenite phase fraction was major factor to the workability of the billet.Copyright

Effect of Welding Condition on Tensile Properties of Friction Stir Lap Joint of Dissimilar Al Alloy, KS5J32/AA6K31

Abstract The focus of this investigation is to evaluate the effect of joining parameter on the microstructure and mechanical properties of welds produced by friction stir lap welding. The dissimilar Al alloys, KS5J32 and AA6K31, were joined by friction stir lap welding technique under several welding conditions, and KS5J32 alloy was placed on the top of AA6K31 alloy. The tool rotation speeds were 1000, 1250, and 1500rpm, and the welding speeds were 100, 300, 500, 700mm/min, respectively. The results showed that two shapes of nugget, such as onion ring and irregular vortex type, were observed with various revolutionary pitch. In all welding conditions, fracture occurred at the soften region of bottom sheet(AA6K31) and the strengths were 64~78% of those of base metal. Fractured positions were classified into three types : HAZ, triple point, void depending on the revolutionary pitch. The actual thickness of specimen at the fractured location was decreased with decreasing heat input. A linear relationship exists between the effective thickness of fractured position and peak load.Key Words : Friction stir welding, Lap Joint, Dissimilar aluminum alloy, KS5J32, AA6K31, Tensile shear test

Dissimilar Friction Stir Welding of Aluminum Alloys

, 개발 초기부터 현재까지 주로 알루미늄 합금에 적용되었고, 자동차, 항공기, 철도차량, 선박, 로켓연료탱크와 같은 수송분야에 상업화되어 사용되고 있다. 특히 자동차 산업분야에서는 차체경량화를 이루기 위하여 알루미늄의 수요가 증가하여 엔진, 열교환기, 휠, 서스펜션 암, 범퍼빔 등에 사용되고 있으며, 최근에는 차체에까지 그 적용이 확대되었다. 거의 모든 구조재료를 실제품에 적용할 경우, 두 가지 이상의 재료가 사용되며 이들 간의 접합이 필수적이기 때문에 마찰교반접합의 적용을 여러 분야로 확대하기 위해서는 동종 재료뿐만 아니라 이종 재료의 접합에 대한 좀 더 많은 연구가 요구된다. 특히 자동차 제조 산업에 사용될 수 있는 마찰교반점접합, 겹치기 접합 및 최근 개발된 테일러드 블랭크(Tailor welded blanks, TWBs)의 맞대기 접합과 같은 이종 재료 접합이 필수적인 분야가 늘고 있다. 알루미늄 주조재(casting alloy)와 단련재(wrought alloy) 합금 간의 접합, 열처리계(heat-treatable)와 비열처리계(non-heat-treatable) 합금 간의 접합, 알루미늄기지 금속복합재료(Al-MMC)와 기지합금 간의 접합과 같은 이종 알루미늄 합금 간의 접합, 융점의 차이가 비교적 작은 알루미늄 합금과 마그네슘 합금 간의 접합, 물성의 차이가 많이 나는 알루미늄 합금과 철강재료의 접합 등 서로 기계적 성질 및 화학조성이 상이한 재료들 사이의 접합 및 두께가 다른 재료간의 마찰교반접합 등에 대한 시도와 연구가 활발히 진행되고 있다. 현재까지 자동차 분야의 일부를 제외하고 실제 제품의 생산에 적용되는 이종재료의 접합은 많지 않지만 앞으로 그 수요가 매우 증가할 것으로 예측되며 따라서 이에 대한 보다 체계적인 연구가 필요하다. 기존에 보고된 이종 재료의 마찰교반접합에 대한 연구의 대부분은 접합 조건이나 툴 형상과 같은 공정변수가 접합부에 미치는 영향을 고찰하기 위한 목적이 아니라, 접합 시 툴과 접합부 주위의 재료 유동현상을 확인하기 위한 방법으로 고안되어 사용된 것으로서 그 수가 많지 않고 일반적으로 접합부에 다수의 결함이 존재하였다