• Journal of Welding and Joining
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• 제29권2호
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• pp.80-87
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• 2011

In this study, the friction stir spot welding (FSSW) of Mg alloy sheets has been tried using an apparatus devised with a CNC milling machine to give the precise control of joining condition including tool speed. The probe tool used is made of hard metal and composed of cylindrical shoulder and pin parts. The variation of morphologies formed after the friction stir spot welding depending on the plunge speed of the tool were investigated at each rpm of tool. The history of the temperature distribution and the vertical load induced during the spot welding with friction time were measured by using an Infrared Thermal Imager (THERMA CAMTM SC2000) and a loadcell located below the specimen fixture, respectively. Tensile-shear tests were also performed to evaluate the fracture load of welded specimens. In order to characterize the friction stir spot welding of Mg alloy sheets, the variation of the fracture load was discussed on micrographic observations, temperature distribution during the FSSW according to the plunge speeds of tool.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2015년도 추계학술대회 논문집
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• pp.189-189
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• 2015

In this study, the corrosion resistance and adhesion of electrophoretic paint (E-paint) were studied on AZ31 magnesium alloy pretreated in cerium chemical conversion coating solutions with the addition of various ethanol concentrations. It was found that with increasing ethanol concentration from 0 to 90 percent can decrease the formation of $Mg(OH)_2/MgO$ and increase the formation of nano-crystalline cerium oxides on the coating. Both corrosion resistance and adhesion of E-painted AZ31 increased with increasing ethanol concentration. The best E-paint sample was observed on the sample pretreatment in cerium chemical conversion coating solution with the addition of 80 percent of ethanol. This sample showed an excellent adhesion without paint detached after water immersion test for 500 h at $40^{\circ}C$, and only a few blisters observed at the near scratched sites after 1000 h salt-spray test.

• 소성∙가공
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• 제19권5호
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• pp.277-282
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• 2010

Magnesium alloy has been known as lightweight material in automobile and electronic industry with aluminum alloy, titanium alloy and plastic material. Friction welding is useful to join various metals and nonferrous metals that are difficult to join by such as gas welding, resistance welding and electronic beam welding. In this study, friction joining was performed to investigate mechanical properties of Mg alloy with 20mm diameter solid bar. Also the optimal joining conditions for its application were determined on the basis of tensile test, and hardness survey. The joining parameters were chosen as heating pressure, heating time, upsetting pressure, and upsetting time. Heating and upsetting pressure were executed under the range of 10~40MPa and 20~80MPa, respectively. From the experimental results, optimal joining conditions were determined as follows; rotating speed=2000rpm, heating pressure=35MPa, upsetting pressure=70MPa, heating time=1sec, upsetting time=5sec. Also the hardness of jointed boundary showed as HV50 which was similar to that of base metal at the optimal condition, and it was supposed that zone of HAZ was 8mm. Finally two materials were strongly mixed at interface part to show a well-combined microstructure without particle growth or any defect.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.41-41
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• 2009

To evaluate the applicability of dissimilar joining between Mg and Al alloys in automobile manufacturing process, solid state joining processes such as magnetic pulse welding(MPW), friction stir welding(FSW) and friction spot joining(FSJ) were attempted successfully. MPW process has been concentrated mainly on round section tube to tube and tube to bar welds. AZ31 Mg alloy has been successfully welded to pure Al A1070 as well as to Al alloy A3003. While, for friction stir welding of dissimilar sheet joints, AZ31B/A6061 with the thickness of 2mm were used and a square butt joint with a good quality was obtained at the conditions of 0.8mm/sec of travel speed and tool rotation speed of 850rpm. The maximum tensile strength of 179 MPa, which was about 80 % of the Mg base metal tensile strength, has been obtained. Finally, friction spot joining was attempted to make a dissimilar lap joint between AZ31(0.8mm) and A6061(1mm), while the joint exhibited the same level of tensile shear strength as that of similar Mg joint.

• 한국재료학회지
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• 제26권10호
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• pp.513-520
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• 2016

The effect of NaOH concentration on the properties of electrolytic plasma processing (EPP) coating formed on AZ61A Mg alloy is studied. Various types of EPP were employed on magnesium alloy AZ61A in a silicate bath with different concentrations of NaOH additive. Analysis of the composition and structure of the coating layers was carried out using an X-ray diffractometer (XRD) and a scanning electron microscope (SEM). The results showed that the oxide coating layer mainly consisted of MgO and $Mg_2SiO_4$; its porosity and thickness were highly dependent on the NaOH concentration. The Vickers hardness was over 900 HV for all the coatings. The oxide layer with 3 g/l of NaOH concentration exhibited the highest hardness value (1220 HV) and the lowest wear rate. Potentiodynamic testing of the 3 g/l NaOH concentration showed that this concentration had the highest corrosion resistance value of $2.04{\times}10^5{\Omega}cm^2$; however, the corrosion current density value of $5.80{\times}10^{-7}A/cm^2$ was the lowest such value.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2009년도 추계학술대회 초록집
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• pp.105-106
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• 2009

AZ31 (3% Al, 1% Zn) Mg 판재의 내식성 향상을 위해 Ti/Zr/Polymer 복합계의 Cr-free 화성처리 방법을 이용하였다. 염수분무시험을 통해 최고 72시간 ($5{\sim}10%$ 발청) 내식성이 나타남을 확인하였다. 화성피막의 내식성은 그 피막이 가진 성분, 균일도, 치밀도, 형상 및 두께에 의해 좌우되는 만큼 TEM, SEM을 통해 화성피막 구조가 내식성과 어떠한 관련이 있는지 조사하였다. 또한, 화성처리 전 단계 공정인 탈지와 산세 및 중화 공정의 변수 조절을 통해 전처리 공정이 최종 화성피막의 물성에 어떠한 영향을 미치는지 조사하였다. 탈지조건을 $35{\sim}40^{\circ}C$, 5분에서 $50{\sim}80^{\circ}C$, $10{\sim}20$분으로 변경 시 좀 더 균일한 외관을 얻을 수 있었고, 적절한 중화제 선택을 통해 화성피막을 균일하게 형성시킬 수 있었다. 투과전자현미경 결과로 미루어 화성피막의 두께보다 균일도와 치밀도가 내식성에 결정적인 영향을 미치는 것을 확인할 수 있었다.

• 한국주조공학회지
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• 제32권2호
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• pp.75-80
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• 2012

In this study, we are aimed to prevent grain growth of semi-solid AZ31 magnesium alloys during reheating process. The semi-solid AZ31+(Ca) billets were investigated by using metallographic analysis, X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy in order to elucidate the effect of Ca addition during reheating process. The grain growth of semi-solid AZ31+(Ca) billet was reduced with increasing Ca content during reheating. The grain size of AZ31+(Ca) billet decreased with increasing volume fraction of Al2Ca particles. The grain growth rate constant K calculated by Oswald ripening LSW theory in AZ31+1.5wt.% Ca billet was the lowest 129.

• 한국결정성장학회지
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• 제28권2호
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• pp.80-84
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• 2018

AZ31과 AZ91 Mg 합금을 Na-P 및 Na-Si 전해질을 사용하여 전해질의 농도, 인가전압, 처리시간에 따라 여러가지 조건에서 PEO 처리하여 5%의 농도를 갖는 염수분무법으로 내부식성 연구를 하였다. 일반적으로 산화피막 코팅 두께가 증가하면 내부식성이 증가하였다. 코팅두께보다 산화피막 표면의 기공크기가 커지면 장기 내부식성은 나빠지는 경향을 보인다. 산화피막의 전체적인 산화물 결정상이 증가할수록, 또 MgO 결정상 대신 $Mg_2SiO_4$ 상과 같은 다른 결정상이 증가할수록 내부식성이 월등히 증가하는 것을 알 수 있었다.