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주조 및 불연속 석출물 미세조직을 가지는 Mg-Al 합금의 진동감쇠능
전중환,Jun, Joong-Hwan 한국열처리공학회 2021 熱處理工學會誌 Vol.34 No.5
In this study, damping capacities were comparatively investigated for Mg-9%Al alloy with as-cast (AC) and fully discontinuous precipitates (DPs) microstructures, respectively. The DPs microstructure was obtained by solution treatment at 678 K for 24 h, followed by furnace cooling to RT. The AC microstructure was typically characterized by partially divorced eutectic β(Mg<sub>17</sub>Al<sub>12</sub>) phase particles distributed along the α-(Mg) matrix cell boundaries. The DPs microstructure showed lamellar morphology consisting of α and β thin layers with various interlamellar spacings. The DPs microstructure had better damping capacity than the AC microstructure in the strain-amplitude independent region, while in the strain-amplitude dependent region, the damping behavior was reversed. In view of the microstructural features of AC and DPs, the lower concentration of Al in the α-(Mg) phase for the DPs microstructure and the lower β phase number density for the AC microstructure would be responsible for the higher damping capacities in the strain-amplitude independent and strain-amplitude dependent regions, respectively.
Mg-Al-Zn 합금에서 불연속 석출물의 층상 구조와 경도에 미치는 냉각 속도의 영향
전중환,Jun, Joong-Hwan 한국열처리공학회 2020 熱處理工學會誌 Vol.33 No.6
The relationship between the hardness and interlamellar spacing of discontinuous precipitates (DPs) formed by continuous cooling was studied for Mg-9%Al-1%Zn alloy. After solution treatment at 683 K for 24 h, the specimens were cooled to room temperature with different cooling rates ranging from 0.2 to 2 K·min<sup>-1</sup>, in order to obtain DPs with various interlamellar spacings. It was found that cooling rate of 2 K·min<sup>-1</sup> yielded only small amount of nodular DPs at the grain boundaries, while cooling rates below 2 K·min<sup>-1</sup> yielded both DPs and continuous precipitates (CPs). The volume fraction of DPs increased with increasing cooling rate up to 0.5 K·min<sup>-1</sup>, over which it abruptly decreased. The hardness of DPs was increased with an increase in the cooling rate, whereas the interlamellar spacing of the DPs was decreased with respect to cooling rate. The hardness of the DPs formed by continuous cooling was correlated with the interlamellar spacing and can follow a Hall-Petch type relation as in the case of pearlite with lamellar morphology.
용체화처리된 Mg-4%Zn 합금의 부식 저항성에 미치는 미량 Ca 첨가의 영향
전중환,황인제,Jun, Joong-Hwan,Hwang, In-Je 한국열처리공학회 2016 熱處理工學會誌 Vol.29 No.4
Influence of trace amount of Ca addition on the corrosion resistance was comparatively investigated in solutionized Mg-4%Zn and Mg-4%Zn-0.1%Ca alloys. In as-cast state, the alloys were characterized by primary ${\alpha}-(Mg)$ dendrite with MgZn intermetallic compound particles. After solution-treatment, both alloys consisted of single ${\alpha}-(Mg)$ phase by dissolution of the compound particles into the matrix. It was found from the immersion and electrochemical corrosion tests that the Mg-4%Zn alloy had better corrosion resistance than the Mg-4%Zn-0.1%Ca alloy. Morphological and compositional analyses on the surface corrosion products indicate that the incorporation of Ca oxide with low PBR value into the surface corrosion products would be responsible for the decreased corrosion resistance of the Ca-containing alloy.
Fe-17%Mn 합금의 진동감쇠능에 미치는 ε 마르텐사이트 함량과 진폭변형율의 영향
전중환,이영국,최종술 ( Joong Hwan Jun,Young Kook Lee,Chong Sool Choi ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.2
The effects of ε martensite content and strain amplitude on damping capacity of an Fe-17%Mn alloy have been studied to establish damping mechanism of Fe-Mn system corresponding to the magnitude of strain amplitude. In a range of 1×10^(-4)∼3×10^(-4) strain amplitude, the damping capacity is linearly proportional to the ε martensite content, which suggests that stacking faults and ε martensite variant boundaries are the principal damping sources. In the range of 4×10^(-4)∼6×10^(-4) strain amplitude, however, a maximum damping capacity is observed around 68 vol% ε. This behavior is very similar to dependence of relative area of γ/ε interface on ε martensite content. This means that in this strain range, γ/ε interface acts as damping source in addition to the stacking faults and variant boundaries in Fe-17%Mn alloy.
전중환,Jun, Joong-Hwan 한국열처리공학회 2017 熱處理工學會誌 Vol.30 No.6
The effect of cooling rate on the damping capacity of pure Mg was studied. Two Mg samples with different cooling rates were prepared by heat treatment at 873 K for 24 h, followed by water quenching and by furnace cooling to room temperature, respectively. The average grain sizes of the Mg samples were almost identical regardless of the cooling rate, but more twins were observed in the sample with faster cooling rate. The calculated vacancy fraction was higher in the fast cooling sample than the slow cooling one. It is noted that the fast cooling sample exhibited lower damping capacity both in the strain-amplitude independent and strain-amplitude dependent regions. Higher values of vacancy concentration and number density of twins in the fast cooling sample are considered to be responsible for the deteriorated damping capacity in the strain-amplitude independent and strain-amplitude dependent regions, respectively.
Fe-Mn 합금에서 γ→ε마르텐사이트 변태의 Ms온도에 미치는 오스테나이트 결정립크기의 영향
전중환,최종술 ( Joong Hwan Jun,Chong Sool Choi ) 한국열처리공학회 1997 熱處理工學會誌 Vol.10 No.2
Effect of sustenite grain size on starting temperature of γ→ε martensitic transformation(M_s) has been studied in an Fe-18%Mn alloy. Particular attention was paid on the variation of stacking fault energy with austenite grain size, which is considered to be a important factor affecting γ→ε martensitic transformation. Austenite grain size was increased in a wide range from 13,um to 185 with increasing solution treatment temperature from 700℃ to 1100℃. Hardness was decreased with increasing austenite grain size while the volume fraction of a martensite showed a reverse tendency, which indicates that the hardness is more dependent on austenite grain size thane martensite content. No significant change was found in M_s temperature when the grain size was larger than about 30㎛. In case that, the austenite grain size was smaller than about 30㎛, however, M_s temperature was marlkedly decreased with decreasing austenite grain size. A linear relationship between M_s temperature and the stacking fault formation probability, i.e. the reciprocal of the stacking fault energy was obtained, which suggests that the variation of M_s temperature with austenite grain size is closely related to the change in stacking fault energy.
등온 시효한 Mg-Al-(Zn) 합금에서 불연속 석출물의 경도와 미세조직에 미치는 Zn 첨가의 영향
전중환 ( Joong-hwan Jun ) 한국열처리공학회 2022 熱處理工學會誌 Vol.35 No.4
The present study aims to investigate the influence of Zn addition on hardness and microstructural characteristics of discontinuous precipitates (DPs) formed by isothermal aging in Mg-9%Al and Mg-9%Al-1%Zn alloys. To obtain large DPs volume fractions in the microstructure, the alloy specimens were solution-treated at 688 K for 24 h followed by water quenching, and then aged at 413 K for 48 h. The aged Mg-9%Al-1%Zn alloy had higher DPs content than the Mg-9%Al alloy, indicating that the Zn addition plays a beneficial role in enhancing age-hardening response. The DPs in the Zn-containing alloy possessed the higher hardness than those of the Zn-free alloy. Microstructural examination revealed that the increased hardness of the DPs resulting from the Zn addition is closely associated with the lower α-(Mg)/ β(Mg<sub>17</sub>Al<sub>12</sub>) interlamellar spacing and the higher volume fraction of β phase layer of the DPs. (Received June 23, 2022; Revised July 6, 2022; Accepted July 11, 2022)
AZ91-CaO 합금의 미세조직과 인장 특성에 미치는 열처리의 영향
전중환 ( Joong Hwan Jun ) 한국열처리공학회 2012 熱處理工學會誌 Vol.25 No.4
This study aims to investigate and compare the microstructures and room temperature tensile properties for AZ91 and ECO-AZ91(AZ91+0.3%CaO) alloys in as-cast, T4 and T6 states, respectively. In as-cast state, the ECO-AZ91 alloy has finer microstructure than the AZ91 alloy. The AZ91 alloy exhibits greater ductility, while YS and UTS are inferior to those of the ECO-AZ91 alloy. After T4 treatment, most of b compounds disappear in the AZ91 alloy, whereas b phase is still observed in the ECO-AZ91 alloy due to its enhanced thermal stability, resulting in lower values of ductility and UTS. In T6 state, YS and UTS are better in the ECO-AZ91 alloy.
Mg-Al 합금에서 연속 냉각 및 등온 시효로 생성된 불연속 석출물의 미세조직 특징과 경도
전중환 ( Joong-hwan Jun ) 한국열처리공학회 2020 熱處理工學會誌 Vol.33 No.4
The purpose of this study was to investigate comparatively the microstructural characteristics and hardness of discontinuous precipitates (DPs) in Mg-9%Al alloy, which were formed by continuous cooling (CC) from 678 K to RT and isothermal aging (IA) at 413 K, respectively. In as-cast state, the Mg-9%Al alloy consisted of partially divorced eutectic β(Mg<sub>17</sub>Al<sub>12</sub>) particles with a small amount of DPs showing (α+β) lamellar morphology adjacent to the β particles. The DPs formed by CC had interlamellar spacings in a broad range of 0.85~2.12 ㎛ (1.51 ㎛ in average) owing to the various formation temperatures in response to continuous cooling process. Meanwhile, the DPs formed by IA had relatively narrower interlamellar spacings of 0.14~0.29 ㎛ (0.21 ㎛ in average), which is associated with the low and constant formation temperature. Thinner and higher volume fraction of β phase layers were noticeable in the DPs formed by IA. Higher hardness values were obtained in the DPs formed by IA than the DPs formed by CC, which may well be ascribed to the finer lamellar structure and higher β phase content of the DPs formed by IA. (Received June 15, 2020; Revised June 23, 2020; Accepted June 29, 2020)