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AZ31B 마그네슘 합금 판재의 Galling특성에 미치는 금형소재와 온도의 영향
권혁우(H. Gwon),김종철(J. C. Kim),정영중(Y.-J. Jeong),김재윤(J. Y. Kim),김용석(Y.-S. Kim) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5
Galling is the most frequently observed gross damage include scratching, grooving and plastic deformation of surfaces of metal sheet (or tools), which is associated with adhesion or stiction during hot forming of magnesium alloys. This study was undertaken to examine tribological phenomena during sliding of tool steel against AZ3l B Mg alloy and to find out formation mechanism of the galling. Reciprocating sliding of tool steel against the Mg-alloy plate was carried out at various temperature and normal loads under an un lubricated condition. The galling behavior was evaluated by measuring friction coefficient and surface roughness together with SEM observation. Higher and severely fluctuating friction coefficient was measured during sliding at 250℃ than at room temperature. The high and largely varying friction coefficient at 250 ℃ was explained by enhanced adhesion between the two surfaces and easier plastic deformation of the Mg alloy at high temperature.
Mg 합금 판재성형 중 발생하는 galling 현상과 마찰계수와의 상관관계
권혁우(H. Gwon),김명곤(M. G. Kim),허하리(H. L. Hur),김용석(Y.-S. Kim) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.10
Correlation between galling which occurs during Mg alloy sheet forming using a steel die and friction coefficient measured during the sheet forming was investigated. Sliding friction (and/or wear) characteristics of the sliding couples including AZ31B Mg alloy and STD61 tool steel were evaluated using a disk-on-flat friction tester at 250℃. Both a Mg alloy sheet without any pretreatment and the alloy sheet with Mg(OH)₂ film on a surface were tested. Tribological behavior of the Mg alloy sheets slid against bare and DLC coated STD61 tool steel were examined in this study. Galling, which related with a material-transferring, was found to be controlled by mechanisms of adhesive junction forming, shear deformation and fracture of the junctions. The mechanisms also control the degree of resistance against relative sliding between the couples, which was measured as a friction coefficient. The correlation between the galling and the friction coefficient was discussed.
권혁우(H. Gwon),허하리(H. L. Hur),구본우(B. W. Gu),김종국(J. K. Kim),강용진(Y. J. Kang),김용석(Y. -S. Kim) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.10
Tribological characteristics of a-C:H coating and ta-C coating against AZ31 Mg alloy was investigated. The a-C:H coating was deposited on a STD-61 steel pin by the plasma-enhanced chemical-vapor deposition (PECVD) process. The hydrogen-free DLC (ta-C) was prepared by filtered vacuum arc deposition (FCVA). Dry sliding friction and galling characteristics of the two DLC coatings on the STD-61 steel against AZ31 Mg alloy disks were evaluated using a reciprocating sliding tribometer at room temperature and at 250 ℃. To represent a real sliding during the sheet metal forming process, single-stroke tests were adapted (10 mm of stroke length) rather than a reciprocating long sliding-distance test. Both a-C:H coating and ta-C coating suppressed the adhesion between the Mg alloy and the tool steel at room temperature, which kept the friction coefficient low. However, at 250 ℃, both DLC coatings exhibited severe adhesion to the Mg alloy, which increased the friction coefficient and the galling.
AZ31B 마그네슘 합금 galling 기구에 미치는 온도와 하중의 영향
권혁우(H. Gwon),정영중(Y.-J. Jeong),김누리(N.R. Kim),김용석(Y.-S. Kim) 한국소성가공학회 2013 한국소성가공학회 학술대회 논문집 Vol.2013 No.10
Galling is the most frequently observed tribological phenomena during sheet metal forming, which is associated with adhesion (stiction) and transferring of a metallic particle from softer sheet metal to harder tool surface. In this study, tribological characteristics during sliding of STD-61 tool steel against AZ31B magnesium alloy were examined to find out galling mechanism of AZ31B magnesium alloy-tool steel tribopair at different loads and temperatures. Flat surface-on-disk reciprocating tests were carried out at various applied loads under both dry and lubricated condition at room temperature and 250 ℃. Galling of the AZ31B magnesium alloy was evaluated by measuring friction force (friction coefficient), surface roughness and observing slid surfaces of both Mg alloy and tool steel by OM and SEM. The results showed that number of asperity junctions formed between the two surfaces increased rapidly as temperature and applied load increase. Severe plastic deformation was observed at the slid surface of the AZ31B magnesium alloy sheet.
금형 강 표면 처리에 따른 AZ31B 마그네슘 합금 판재 Galling 거동의 변화
권혁우(H. Gwon),정영중(Y. -J. Jeong),김고남(G. Kim),김재윤(J. Y. Kim),김명곤(M. G. Kim),김용석(Y. -S. Kim) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.10
In this study, tribological phenomena and galling mechanisms of tool steel coated with various coatings (DLC, CrN and TiN) were examined during sliding against AZ31 B Mg alloy. Reciprocating sliding of the coated tool steel against the Mg alloy plate was carried out at various temperatures under an un lubricated condition. The galling behavior was evaluated by measuring friction coefficient and surface roughness together with SEM observation. Higher and severely fluctuating friction coefficient (stick-slip oscillations) was measured when the Mg particles are transferred from the alloy plate to the tool steel surfaces. DLC coating showed improved anti-galling properties at room temperature during the sliding. However, at high temperature, the coating did not reduce galling and related tribological interactions between the coated steel and the Mg alloy. CrN and TiN coatings showed poor galling characteristics at room temperature compared with uncoated tool steels.
마그네슘 합금에 대한 DLC 코팅의 온도에 따른 마찰기구 해석
권혁우(H. Gwon),김명곤(M.G. Kim),허하리(H.L. Hur),김용석(Y.-S. Kim) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
The sheet-forming of Mg alloys is carried out at elevated temperature (250 ℃) due to their low formability at room temperature. The high-temperature process results in a typical surface damage, the galling. In this investigation, tribologcial characteristics of DLC coating which had been widely used for low-friction processes against AZ31 Mg alloy were investigated. Dry sliding friction and galling characteristics of AZ31 Mg alloy disks which were slid against uncoated and DLC-coated STD-61 steel pin were evaluated using a reciprocating sliding tribometer at room temperature and 250 ℃. To represent a real sliding during the sheet metal forming process, single-stroke tests were adapted (10 mm of stroke length) rather than a reciprocating long sliding-distance test. The DLC coating suppressed adhesion between the alloy and the tool steel at room temperature, which kept the friction coefficient low. However, at 250 ℃, severe adhesion occurred between the two surfaces, which increased the friction coefficient and the galling.
마그네슘 합금의 판재 성형 시 금형-판재간 응착문제 해결을 위한 표면처리
권혁우(H. Gwon),김명곤(M.-G. Kim),허하리(H.-L. Hur),박영희(Y.-H. Park),김용석(Y.-S. Kim) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.5
In this study, surface of a AZ31B Mg alloy sheet was coated with Mg(OH)₂ film and its tribological characteristics were evaluated during hot forming. The coating was applied to the sheet with a hope of avoiding tribological problems during sheet forming the alloy sheet such as wear, stciking and galling of forming tools and sheets. Flat surface-on-disk reciprocating tests were carried out using the AZ31B Mg alloy sheet and STD-61 tool steel as the surface and the disk, respectively. The tests were performed at various applied loads under both dry and lubricated condition at room temperature and 250℃. Tool steel disks with PVD coatings were also evaluated. Galling of the AZ31B magnesium alloy sheet was examined by measuring friction coefficient, surface roughness and observing slid surfaces of both the Mg alloy sheet and coated tool surface by OM and SEM. The Mg(OH)₂ film reduced friction coefficient and effectively suppressed galling of the Mg alloy sheet.
열처리된 2024A1 합금의 석출물이 건식 미끄럼 마멸 특성에 미치는 영향
권혁우(H.W. Gwon),윤나래(N.R. Yoon),김종철(J.C. Kim),정영중(Y.-J. Jung),김용석(Y.-S. Kim) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.5
In the present study, the effect of precipitates on the dry sliding wear characteristics of 2024 A1 alloy was investigated. Dry sliding wear tests were performed on the as-received (T4) and solution treated 2024 A1 alloy, and their wear behavior was compared in connection with work hardening behavior during the wear. Special attention was given to the relationship between strain hardening and the precipitates, which changed the wear rate and characteristics of the alloy. Work-hardening at the wearing surface is the most important factor during sliding wear of metallic materials, since the strain hardening affects the formation of a deformation layer at the surface. The deformation layer is often related with the formation of wear particles which are detached particles from the layer. The hardened deformation layer also acts as a protecting layer that resists further progress of wear. The relationship between the microstructure and the strain-hardening at the wearing surface was explored, which explained the wear-rate variation with the microstructure.