• 한국주조공학회지
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• 제26권5호
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• pp.211-216
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• 2006

The study for thixoextrusion process of 7075, 7003 Al wrought alloys and AZ31 Mg wrought alloy was carried out with respect to reheating rate, isothermal holding temperature and time with an emphasis to the effect of homogenization on thixotropic micro-structures during the partial remelting, especially in the low liquid fraction ($f_L<0.2$). The liquid fraction and average grain size with respect to reheating profile such as reheating rate, isothermal holding temperature and time were almost uniform. It is considered very useful for thixoextrusion in terms of process control such as billet temperature control and actual extrusion time. Micro-structural controls of 7075, 7003 Al wrought alloys and AZ31 Mg wrought alloy before and after homogenization were available and thixotropic microstructures were obtained in both specimens.

• 한국주조공학회지
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• 제25권6호
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• pp.249-253
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• 2005

The present study focuses on 7075 aluminum wrought alloy to investigate the potential industrial applications of thixoextrusion process. The microstructural evolution of 7075 aluminum wrought alloy for thixoextrusion has been investigated as a function of isothermal holding temperature and time in the partially remelted semisolid state. The results showed that the liquid fraction increased with increasing isothermal holding temperature and time while the average grain size was inversely proportional to isothermal holding temperature and time up to 5min. However, there was no big change of liquid fraction and average grain size with respect to isothermal holding temperature and time. The important fact that the liquid fraction and average grain size were almost uniform after 5 min holding time is considered very useful for thixoextrusion in terms of process control.

• Journal of Welding and Joining
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• 제34권6호
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• pp.69-74
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• 2016

Because the pure titanium has superior corrosion resistance and formability compared with different material, it is widely used as material of welded heat exchanger. When the welding of heat exchanger is carried out, certain area in which welding start and end are overlapped occurs. The humping of back bead is formed in the overlap area due to partial penetration. Thus in this study, the experiments were carried out by changing the length and wave shape of overlap area, and then the weldabiliay was evaluated through the observation of microstructure, the measurement of hardness and tensile-shear strength test in the overlap area. When overlap length was 9.8mm, humping bead was suppressed. The microstructure of overlap area coarsened and its hardness increased due to remelting. As a result of tensile-shear strength test in the overlap area according to applying the wave shape control, it was confirmed that the overlap area applied wave shape control had more excellent yield strength and ductility.

• Journal of Welding and Joining
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• 제33권5호
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• pp.53-60
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• 2015

Laser surface Melting Process is getting hardening layer that has enough depth of hardening layer as well as no defects by melting surface of substrate. This study used CW(Continuous Wave) Yb:YAG and STD11. Laser beam speed, power and beam interval are fixed at 70mm/sec, 2.8kW and 800um respectively. Hardness in the weld zone are equal to 400Hv regardless of melting zone, remelting zone overlapped by next beam and HAZ. Similarly, microstructures in all weld zone consist of dendrite structure that arm spacing is $3{\sim}4{\mu}m$, matrix is ${\gamma}$(Austenite) and dendrite boundary consists of ${\gamma}$ and $M_7C_3$ of eutectic phase. This microstructure crystallizes from liquid to ${\gamma}$ of primary crystal and residual liquid forms ${\gamma}$ and $M_7C_3$ of eutectic phase by eutectic reaction at $1266^{\circ}C$. After solidification is complete, primary crystal and eutectic phase remain at room temperature without phase transformation by quenching. On the other hand, microstructures of substrate consist of ferrite, fine $M_{23}C_6$ and coarse $M_7C_3$ that have 210Hv. Microstructures in the HAZ consist of fine $M_{23}C_6$ and coarse $M_7C_3$ like substrate. But, $M_{23}C_6$ increases and matrix was changed from ferrite to bainite that has hardness above 400Hv. Partial Melted Zone is formed between melting zone and HAZ. Partial Melted Zone near the melting zone consists of ${\gamma}$, $M_7C_3$ and martensite and Partial Melted Zone near the HAZ consists of eutectic phase around ${\gamma}$ and $M_7C_3$. Hardness is maximum 557Hv in the partial melted zone.

• 자원환경지질
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• 제23권1호
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• pp.35-57
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• 1990

This study has been carried out on the Pegmatites, Naedeogri Granites, Nonggeori Granites and Metasedimentary rocks in the middle area of Taebaeksan region to investigate the geochemical properties and possibility of productivity. Pegmatites are characterized by metamorphosed anatectic pegmatite and differentiated magmatic pegmatite, and are mixed type of rare-element pegmatite and mica-bearing pegmatite by the classification of Ginsburg(1979). The petrological type of the igneous rocks is thought to be calcalkali, subalkaline and peralumious. According to chemical variations against D. I., differentiation trends from Naedeogri and Nonggeori Granites through non-mineralized pegmatites to mineralized pegmatites are supposed. From the relationship between oxided and $SiO_2$, pegmatites and Nonggeori Granite have shown similar tendencies and bulk composition of pegmatites and similar to metasedimentary rocks near the intrusives. By judging the correlations of trace elements, it is elucidated that pegmatites adjacent to Naedeogri and Nonggeori Granites have been originated in magma differentiation from these granites and the others have been differentiated by remelting or partial melting from metasedimentary rocks. $Sp_5$, $Sp_8$, and $Sp_9$ pegmatites are considered as productive rocks, and $Sp_4$, $Sp_6$, $Sp_7$, $Sp_{10}$, $Sp_{11}$, and $Sp_{12}$ pegmatites and granites are supposed to have a weak productivity, in terms of element ratios related with Sn mineralizations. Tourmalines in productive pegmatites are formed under the circumstance of Li-poor granitoids and associated with pegmatites, and the others are seemed to be originated in metapelites and metapsammites which are not coexisting with an Al-saturating phase. Three types of chemical zoning are noticed in tourmalines: (1) apparently homogeneous compositional patterns, (2) a continuous core-to-rim zoning and, (3) a discontinuous core-to-rim zoning. From results of EPMA of tourmalines, Al, Mg and Ca increase closer to rim, while Fe decreases.

• 자원환경지질
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• 제28권6호
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• pp.623-633
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• 1995

번암광산은 소백산 육괴의 남서부에 위치하며, 소백산은 편마암 복합체를 $N20{\sim}30^{\circ}E$ 방향으로 관입하여 나타난다. 주변 화강암들은 변성화강암류의 재용융 혹은 부분용융에 의해 생성된 calc-alkaline계열의 마그마로부터 분화 생성된 산화물로 추정된다. 광상을 배태시킨 광화용액을 화강암체를 형성한 마그마로부터 유래하였다해도 시기적으로 훨씬 후기에 생성되었을 것이다. 공생광물군에 대한 연구결과 광화작용은 크게 3시기로 I기: 기저 유화광물의 생성시기, II기: 후기 유화광물, 엘렉트럼 및 함은 유영 광물의 생성시기, III기: 소량의 함은 광물, 백색석영 및 탄산염광물의 생성시기로 나눌 수 있다. 번암광산의 생성온도, 염농도 및 압력은 광물공생과 화학성분, 유체포유물, 유황동위원소 지질온도계를 이용하여 측정되었으며 다음과 같다. I기: $200{\sim}315^{\circ}C$. 3.5~6.5 NaCl eq. wt.%. 0,28~0.61 Kbar. II기: $150{\sim}235^{\circ}C$, 4.5~7.4 NaCl eq. wt.%. 0.11~0.15 Kbar로 나타난다. 초기 광화작용동안산소와 유황분압은 각각, $10^{-35.1}{\sim}10^{-39.7}$ atm., $10^{-11.0}{\sim}10^{-13.4}$atm. 으로 나타난다. 이와 같은 연구결과 번암광산은 polymetallic meso-epithermal type의 광상으로 생각된다.

• 자원환경지질
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• 제20권1호
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• pp.35-60
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• 1987

한국(韓國)에 분포(分布)하는 지질시대(地質時代)와 공간(空間)을 달리하는 대표적(代表的)인 15개(個)의 화강암체(花崗岩體)를 대상(對象)으로 광물(鑛物) 및 주(主) 미량(微量) 원소(元素) 지화학적(地化學的) 특징(特徵)을 밝히고 암석성인(岩石成因)과 지체구조진화(地體構造進化)와 연관시켜 연구(硏究)하였다. 그 암석지화학적(岩石地化學的) 특징(特徵)을 바탕으로 선(先)캄브리아기(紀) 화강암(花崗岩), 쥬라기(紀) 화강암(花崗岩)(cratonic과 mobile belt)와 백악기(白堊紀)~제삼기(第三紀) 화강암(花崗岩)으로 구분(區分)된다. 선(先)캄브리아기(紀) 화강편마암(花崗片麻岩)(I-형(型) 및 티탄철석계열(鐵石系列))은 지화학적(地化學的)으로 진화(進化)된 화강암류(花崗岩類)가 변성작용(變成作用)을 받아서 형성(形成)되었으며, 선(先)캄브리아기(紀) 화강암(花崗岩)(S-형(型) 및 티탄철석계열(鐵石系列))은 퇴적기원(堆積起源)의 변성암류(變成岩類)가 부분용융(部分熔融)되어 생성(生成)된 것으로 사료(思料)된다. 쥬라기(紀) 화강암(花崗岩)(S-형(型) 및 티탄 철석계열(鐵石系列))은 주(主)로 하부지각(下部地殼)의 변성퇴적암(變成堆積岩)이 부분용융(部分熔融)되어 형성(形成)되었다. 또한, 백악기화강암(白堊紀花崗岩)(I-형(型) 및 자철석계열(磁鐵石系列))은 하부지각(下部地殼) 또는 상부(上部)맨틀의 화성원암류(火成源岩類)로부터 생성(生成)된 마그마의 분별(分別) 결정작용(結晶作用)으로 결정화(結晶化)되었음이 밝혀졌다. 퍼다이트질(質) 알카리장석(長石)의 용리(溶離)(exsolution)에 의(依)한 지질온도계(地質溫度計)는 선(先)캄브리아기(紀) 및 쥬라기(紀) 화강암(花崗岩)은 각(各) 암체내(岩體內) 그 온도변화폭(溫度變化幅)이 작으며(${\pm}20{\sim}30^{\circ}C$), 약(約) 3~5kbar의 가상압력하(假想壓力下)에서 $315{\sim}430^{\circ}C$의 낮은 온도조건(溫度條件)에서 화학적(化學的) 평형(平衡)을 이룬것으로 나타났다. 이는 화강암관입시(花崗岩貫入時) 주위모암(母岩)들은 광역변성작용(廣域變成作用)과 같은 열류량(熱流量)이 높은 영역하(下)에 있었으며, 그 후(後) 모암(母岩)은 화강암(花崗岩)과 함께 천천히 냉각(冷却)되었기 때문인 것으로 생각된다. 그러나, 백악기(白堊紀) 화강암(花崗岩)들은 각(各) 암체(岩體)마다 1~3kbar 압력하(壓力下)에서 $520^{\circ}C$의 온도(溫度)에서 평형(平衡)을 이루었으며 그 변화폭(變化幅)(${\pm}110^{\circ}C$)이 크다는 것으로 밝혀졌는데, 이는 친(親)마그마가 지표(地表)가까운 천처(淺處)까지 관입(貫入)하여 급속(急速)히 결정화(結晶化)되었음을 시사(示唆)한다. 장석(長石)이 정출(晶出)될때의 산소분압(酸素分壓)은 옥천변성대(沃川變成帶)에 분포(分布)하는 쥬라기(紀) 화강암(花崗岩)이 가장 낮고, 경상분지(慶尙盆地)의 백악기(白堊紀) 화강암(花崗岩)에서 높은 것으로 밝혀졌다. 쥬라기(紀) 화강암(花崗岩)(Hercyno-형(型))은 큐라-퍼시픽(Kula-Pacific)판(板)이 빠른속도(速度)로 북서(北西)쪽으로 밀려와서 대륙간분지(大陸間盆地)(Intracontinental basin)인 옥천분지(沃川盆地)가 closing-collision으로 지각하부(地殼下部)의 부분용융(部分熔融)에 의(依)하여 형성(形成)된 마그마(Wet magma)로 부터 형성(形成)된 후(後) 주위 모암(母岩)과 함께 융기(隆起)되었다. 백악기(白堊紀) 화강암(花崗岩)(Andino-형(型))은 큐라-퍼시픽 해영(海嶺)의 Subduction에 의(依)하여 생성(生成)된 마그마(Dry magma)가 구조적(構造的) 약선대(弱線帶)를 따라 빠른 속도(速度)로 지각천처(地殼淺處)까지 관입(貫入)되었다.