• Advances in materials Research
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• 제7권2호
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• pp.105-118
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• 2018

Magnesium and its alloys are attracted towards all engineering applications like automotive, marine, aerospace etc. due to its inherent high strength to weight ratio. But, extensive use of Mg alloys is limited to the current scenario because of low wear and corrosion resistance behavior. However, equal channel angular press is one of the severe plastic deformation technique which has been effective method to improve the wear and corrosion resistance by achieving fine grain structure. In this study, the effect of grain refinement on wear and corrosion resistance of AZ80 Mg alloys were investigated. The wear behavior of the coarse and fine-grained Mg alloys was examined through $L_9$ orthogonal array experiments in order to comprehend the wear behavior under varies control parameters. It was shown that ECAPed alloy increased the wear and corrosion resistance of the Mg alloy through the formation of fine grain and uniform distribution of secondary ${\beta}-phase$. Also, the performance of AZ80 Mg alloy for these changeswas discussed through SEM morphology.

• 한국재료학회지
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• 제31권1호
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• pp.38-42
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• 2021

In this study, high temperature wetting analysis and AZ80/Ti interfacial structure observation are performed for the mixture of AZ80 and Ti, and the effect of Al on wetting in Mg alloy is examined. Both molten AZ80 and pure Mg have excellent wettability because the wet angle between molten droplets and the Ti substrate is about 10° from initial contact. Wetting angle decreases with time, and wetting phenomenon continues between droplets and substrate; the change in wetting angle does not show a significant difference when comparing AZ80-Ti and Mg-Ti. As a result of XRD of the lower surface of the AZ80-Ti sample, in addition to the Ti peak of the substrate, the peak of TiAl3, which is a Ti-Al intermetallic compound, is confirmed, and TiAl3 is generated in the Al enrichment region of the Ti substrate surface. EDS analysis is performed on the droplet tip portion of the sample section in which pure Mg droplets are dropped on the Ti substrate. Concentration of oxygen by the natural oxide film is not confirmed on the Ti surface, but oxygen is distributed at the tip of the droplet on the Mg side. Molten AZ80 and Ti-based compound phases are produced by thickening of Al in the vicinity of Ti after wetting is completed, and Al in the Mg alloy does not affect the wetting. The driving force of wetting progression is a thermite reaction that occurs between Mg and TiO2, and then Al in AZ80 thickens on the Ti substrate interface to form an intermetallic compound.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.80-83
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• 2004

High temperature deformation behavior of AZ31 Mg alloy was investigated in this study on the basis of a processing map $(\varepsilon\approx0.6)$. To construct a processing map, compression tests were carried out at wide range of temperatures and strain rates $(T=250\~500^{\circ}C,\;\varepsilon=10^{-4}\~100/s)$. Two regions of high deformation efficiency $(\eta)$ were identified as: (1) a dynamic recrystalization (DRX) domain at $250^{\circ}C$ and 1/s and (2) a superplasticity domain at $450^{\circ}C$ and $10^{-4}/s$. Possible deformation mechanisms operating at high temperature were discussed in relation to the activation energy. A two-stage deformation method was found to be effective in enhancing the superplasticity of AZ31 Mg alloy. From the two-stage deformation method, tensile elongation of $1200\%$ was obtained at the superplastic domain.

• 소성∙가공
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• 제21권4호
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• pp.240-245
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• 2012

With the increasing demand for light-weight materials to reduce fuel consumption, the automobile industry has extensively studied magnesium alloys which are light weight metals. The intrinsic poor formability and poor ductility at ambient temperature due to the hexagonal close-packed (HCP) crystal structure and the associated insufficient number of independent slip systems restricts the practical usage of these alloys. Hot working of magnesium alloys using a forging or extrusion enables net-shape manufacturing with enhanced formability and ductility since there are several operative non-basal slip systems in addition to basal slip plane, which increases the workability. In this research, the thermomechanical properties of AZ80 Mg alloy were obtained by compression testing at the various temperatures and strain rates. Optical microscopy and EBSD were used to study the microstructural behavior such as misorientation distribution and dynamic recrystallization. The results were correlated to the hardening and the softening of the alloy. The experimental data in conjunction with a physical explanation provide the optimal conditions for net-shape forging under hot or warm temperatures through control of the grain refinement and the working conditions.

• 열처리공학회지
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• 제33권2호
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• pp.49-56
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• 2020

Magnesium alloy is a metal with high specific strength and light weight, and is attracting attention as a next generation metal for environmentally friendly automobiles and transportation equipment. However, magnesium alloys have a problem of degrading formability due to the basal texture developed during processing, and their application is limited. Although active researches on the control of textures have been conducted in order to minimize this problem, there is a lack of research on the formation of microstructures and textures according to elemental differences. In this study, AZ61 and AZ80 magnesium alloys were selected to investigate the effects of aluminum addition on the microstructure development of magnesium alloys. This research has proven that the increase of the rolling rate results in the decrease of the average grain size of the two alloys, the increase of the hardness, and the increase of the fraction of twins. As shown on this research below, the basal texture developed strongly as the rolling ratio increased. On the other hand, this research also has proven that the two alloys exhibited different texture strength and distribution tendencies, which could be due to the effects of aluminum addition on work hardening, grain size, and twin behavior.

• 한국산학기술학회논문지
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• 제18권6호
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• pp.263-268
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• 2017

상용 마그네슘 합금의 경우, 상온에서 낮은 성형성을 갖기 때문에, 온간 성형 조건 하에서 성형 공정을 수행하는 것이 일반적이다. 마그네슘 합금은 온간 성형 과정 중에 동적 재결정(dynamic recrystallization, DRX)이 발생하여, 초기 결정립 사이즈가 급격하게 작아지며, 내부 전위 밀도가 낮아지게 된다. 이에 따라, 유동 응력 곡선은 세 단계의 복잡한 변형 경화 및 연화 현상을 보이게 된다. 첫 번째 구간에서는 변형률이 증가함에 따라, 가공 경화에 의해 응력이 증가하는 경향을 보이며, 두 번째 구간에서는 동적 재결정 현상에 의한 가공 연화로 응력이 갑작스럽게 감소한다. 세 번째 구간에서는 가공 경화와 가공 연화 사이의 평형에 의해, 응력이 일정하게 나타난다. 본 연구에서는, 성형 온도 $300^{\circ}C$, 변형률 속도는 0.001, 0.1, 1, 10/sec에서 AZ80 합금의 구성 방정식의 18개 변수들을 체계적으로 최적화하며, 유동 곡선의 정확도를 높일 수 있는 방식에 대해 제안하려고 한다. 또한 AZ80외에 AZ61도 추가적으로 최적화여 본 논문에서 제안한 최적화 방식의 성능을 증명하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.62-65
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• 2008

Extrusion characteristics of Mg alloys were studied experimentally. The Al-Zn-Mg alloys, AZ31, AZ6l, AZ80, and AZ91 were extruded with hot hydrostatic extrusion process. The hydrostatic process was efficient to reduce surface friction and extend steady state region in extrusion which made it more convenient to examine deformation behavior of the alloys avoiding the disturbance caused by temporary contact state between billet and die, and billet and container. High pressure was cooperative to expand forming limit of the alloys which were applied on the billet during the extrusion process. Extrusion limits were traced in temperature and extrusion speed domain with changing composition of the alloying elements. Effects of process parameters on extrusion load and microstructure evolution were investigated also.

• Journal of Welding and Joining
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• 제22권3호
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• pp.56-61
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• 2004

Friction stir weldability of AZ31B Mg alloy was studied using microstructural observation and mechanical tests. Defect free joints was obtained under the condition of 2000rpm-100mm/min. In TMAZ, a lot of twin deformation were observed due to the mechanical effect of the FSW tool and thus relatively high hardness was obtained. In SZ, the twin deformation was disappeared by recovery and the hardness decreased because the. grain structure was coarsened by dynamic recrystallization and grain growth. The Al-Mn precipitates were observed throughout the joint regions. On the other hand, $$\beta$-Mg_{17}Al_{12}$ intermetallic compounds were not observed in either of the zone. The joint efficiency was about 80% and the impact value of the joint was almost equal to that of base metal.

• 소성∙가공
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• 제22권2호
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• pp.108-113
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• 2013

This paper demonstrates the lubricant performance in T-shape hot forging of Mg alloys. This processes induces complex plastic material flow of the initial billet such as simultaneous compression and extrusion deformations. Five lubricants with different amounts of graphite are applied to the T-shape forging at temperatures of 300 and $350^{\circ}C$. As the amount of graphite in the lubricant increases, the extruded depth gradually increases, which improves hot forgeability for Mg alloys. However, the lubricant performance decreases as forging temperature increases from 300 to $350^{\circ}C$. As the punch stroke increases, forgeability is considerably influenced by the lubricant. Thus, the selection of lubricants in hot forging of Mg alloys is critical when plastic deformation is severe.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.77-80
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• 2008

Low-cycle fatigue (LCF) tests were carried out to investigate the effect of loading direction on the cyclic deformation behavior and fatigue resistance of rolled AZ31 magnesium alloy. The as-received alloy showed a strong basal texture indicating that the most of basal planes of hexagonal close-packed structure were located parallel to the rolling direction. Two types of specimens whose loading directions were oriented parallel (RD) and vertical (ND) to the rolling direction. respectively, were used for the comparison. It was found that RD specimens yielded at much lower stresses during compression, while vice versa for the ND specimens, which was mainly attributed to the formation of primary twins. This anisotropic deformation behavior resulted in the different mean stresses during the cycling of RD and ND specimens, affecting the fatigue resistance of two specimens. The ND specimen showed a superior fatigue resistance as compared to the RD specimen under strain-controlled condition.