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Mg-6Zn-xCu 합금의 열적 특성에 미치는 Cu 첨가의 영향
예대희 ( Dea Hee Ye ),김현식 ( Hyun Sik Kim ),강민철 ( Min Cheol Kang ),정해용 ( Hae Yong Jeong ) 한국주조공학회 2015 한국주조공학회지 Vol.35 No.4
In this study, Mg-Zn alloys are investigated in terms of their thermal properties after an addition of Cu. Al element is added to improve the mechanical properties and castability in general case. However, it was excluded here because it significantly decreases the thermal conductivity. On the other hand, Zn was added as a major element, which had less influence on reducing the conductivity and can complement the mechanical properties as well. Cu was also added, and it improved the heat transfer characteristics as the amount was increased. The composition ranges of Zn and Cu are 6 wt.% and 0~1.5 wt.%, respectively. Mg-6ZnxCu alloy was prepared by a gravity casting method using a steel mold and then the thermal conductivity and the microstructure of the as-cast material were investigated. By measuring the density_(ρ), specific heat_(Cp) and thermal diffusivity_(α), the thermal conductivity_(λ) was calculated by the equation λ = ρ·Cp·α. As the amount of Cu increased in the Mg-6Zn-xCu alloy, the heat transfer characteristics were improved, resulting in a synergistic effect which is slow when the added Cu exceeds 1 wt.%. In order to investigate the relative thermal conductivity/emission of the Mg-6Zn-xCu alloy, AZ91 and AZ31 were experimentally evaluated and compared using a separate test equipment. As a result, the Mg-6Zn-1.5Cu alloy when compared to AZ91 showed improvements in the thermal conductivity ranging from 30 to 60% with a nearly 20% improvement in the thermal emission.
Mg-Nd-Y-Zr-Zn 주조합금의 인장특성에 미치는 시효처리의 영향
김현식,예대희,강민철,김인배,Kim, Hyun-Sik,Ye, Dea-Hee,Kang, Min-Cheol,Kim, In-Bea 한국재료학회 2008 한국재료학회지 Vol.18 No.5
Magnesium alloys are alloyed with rare earth elements (Re, Ca, Sr) due to the limited use of magnesium in high-temperature conditions. In this study, the influences of Zr and Zn on the aging behavior of a Mg-Nd-Y alloy were investigated. magnesium alloys containing R.E elements require aging treatments Specifically, Nd, Y and Zr are commonly used for high-temperature magnesium alloys. Various aging treatments were conducted at temperatures of 200, 250 and $300^{\circ}C$ for 0.5, 1, 3, 6, and 10 hours in order to examine the microstructural changes and mechanical properties at a high temperature ($150^{\circ}C$). Hardness and high-temperature ($150^{\circ}C$) tensile tests were carried out under various aging conditions in order to investigate the effects of an aging treatment on the mechanical properties of a Mg-3.05Nd-2.06Y-1.13Zr-0.34Zn alloy. The maximum hardness was 67Hv; this was achieved after aging at $250^{\circ}C$ for 3 hours. The maximum tensile, yield strength and elongation at $150^{\circ}C$ were 237MPa, 145MPa and 13.6%, respectively, at $250^{\circ}C$ for 3 hours. The strengths of the Mg-3.05Nd-2.06Y-1.13Zr-0.34Zn alloy increased as the aging time increased to 3 hours at $250^{\circ}C$ This is attributed to the precipitation of a Nd-rich phase, a Zr-rich phase and $Mg_3Y_2Zn_3$.
김현식 ( Hyun Sik Kim ),예대희 ( Dea Hee Ye ),강민철 ( Min Cheol Kang ),김정대 ( Jung Dae Kim ),정해용 ( Hae Yong Jeong ) 한국주조공학회 2014 한국주조공학회지 Vol.34 No.6
Pure magnesium and magnesium alloys have been applied to various kinds of industrial fields, especially automotive and electronic parts. These parts are manufactured mainly through a diecasting process. These days, magnesium ingots are used as raw material, and recycled ingots are often used for commercial purposes. But the quality of virgin magnesium and recycled ingots is not secure. Therefore, massive casting defects can occur, and some things manufactured can be damaged by these defects. This study evaluated the inclusions of virgin magnesium and recycled ingot. It also included composition analysis by spectrometer, measuring inclusion contents by SEM & EDS, and performing a brightness test on fractured surfaces. The brightness test is generally very easy and obtains results quickly, so its results have been compared with the results obtained from various test methods. From the test results, we obtained a satisfactory result in evaluating inclusion and oxide. The brightness values are lower as the inclusion contents are higher. When the brightness value is over 47 in AM50A and 44 in AZ91D, the mechanical properties are expected to be good.
기술강좌(技術講座) : 마그네슘 주조성형기술의 개발동향
김현식 ( Hyun Sik Kim ),예대희 ( Dea Hee Ye ),강민철 ( Min Cheol Kang ) 한국주조공학회 2011 한국주조공학회지 Vol.31 No.5
Magnesium alloys have many advantages such as light-weight, high machinability, damping capacity, etc. So magnesium alloy parts have been used in transportation, mobile phone, military industries. Because of HCP atomic structure, Magnesium is very difficult in plastic deformation process, so most of magnesium products are fabricated by casting process. Magnesium alloys have low heat-capacity, high fluidity and low Fe solubility. For these reasons it is more suitable than aluminum in mass-production by casting. And various casting technologies have been developed. So casting technologies for magnesium developed recently is discussed in this paper.
김현식 ( Hyun Sik Kim ),예대희 ( Dea Hee Ye ),강민철 ( Min Cheol Kang ),손근용 ( Keun Yong Sohn ),정해용 ( Hae Yong Jeong ) 한국주조공학회 2014 한국주조공학회지 Vol.34 No.1
Magnesium and its alloys are being applied to various kinds of industrial fields, especially their use on automotive parts and electronic part. These parts are manufactured mainly through die casting process and magnesium ingots are used as raw materials. In the case that ingot quality is not secured, massive casting defects can occur and some manufactures can be damaged by the defects. This study is to evaluate ingots` cleanliness of magnesium alloys. It includes composition analysis by spectrometer, measurement of inclusion contents by SEM, brightness test on fractured surface and etc. Especially, the brightness test is a very easy and quick evaluation method. The brightness becomes low when the amount of oxides or inclusions on the surface increases. The brightness test data have been compared with those obtained from other methods for measuring the mount of impurities, which showed good relationship between the brightness and the others. Thus, the brightness test could be a promising method to measure the cleanliness of magnesium alloys.
강민철(Min-Cheol Kang),예대희(Dea-Hee Ye),고근호(Geun-Ho Go) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.4
Metal parts are produced by conventional methods such as casting, forging and cutting, extrusion, etc. However, nowadays, with additive manufacturing (AM), it is possible to directly commercialize by means of stacking of equipment to the 3D drawing and use of high precision tools such as laser source. Thus, drawing of materials is an important aspect in delivering good products. AM deals with production of lighter aircraft parts and few more three-dimensional molds, it wish to manufacture special medical parts and want to steadily expand the new market area. The cost of related equipment and materials are still expensive and difficult to obtain on a mass production. However, the ability to make changes and lead the innovation in the paradigm of traditional manufacturing process is still effective. In this paper, we introduce metal AM and the principles of the related devices, metal powder production process, and their application.