• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.53-56
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• 2006

Magnesium alloy AZ31, which processed by conventional rolling or extrusion, has high anisotropy of mechanical properties in its strength and elongation at room temperature. We compared the influence of differential speed rolling with conventional rolling process on microstructure and mechanical properties of commercial AZ31 sheet. Commercial AZ31 alloy sheets were processed with conventional and differential speed rolling with thickness reduction ratio of 30% at a various temperature. The elongation of AZ31 alloy, warm-rolled by differential speed rolling is larger than those rolled by conventional rolling. Besides, grain size and distribution on microstructure of the conventional rolled materials were coarse and inhomogeneous, on the contrary, those of the differential speed rolled were fine and homogeneous.

• Transactions of Materials Processing
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• v.20 no.2
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• pp.160-166
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• 2011

Weight reduction while maintaining functional requirements is one of the major goals in the automotive industry. The use of lightweight magnesium alloys offers great potential for reducing weight because of the low density of these alloys. However, the formability and the surface quality of the final magnesium alloy product for auto-body structures are not acceptable without a careful optimization of the design parameters. In order to overcome some of the main formability limitations in the stamping of magnesium alloys, a new approach, the so-called "hybrid technology", has been recently proposed for body-in-white structural components. Within this approach, necessary level of mechanical joining can be obtained through the use of lightweight material-steel adhesion promoters. This paper presents the development process of an automotive hybrid hood assembly using magnesium alloy sheets. In the first set of material pairs, the selected materials are magnesium alloy AZ31B alloy and steel(SGCEN) as inner and outer panels, respectively. In order to optimize the design of the inner panel, the stamping process was analyzed with the finite element method (FEM). Laser welding by CW Nd:YAG were used to join the magnesium alloy sheets. Based on the simulation results and mechanical test results of the joints, the determination of die design variables and their influence on formability were discussed. Furthermore, a prototype based on the proposed design was manufactured and the static stiffness test was carried out. The results demonstrate the feasibility of the proposed hybrid hood with a weight reduction of 25.7%.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.55-62
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• 2004

In this study, the effects of Ca content and processing variables on hot rolling properties of gravity cast AZ31-xCa alloys were evaluated systematically. The number and length of side crack were decreased with increasing preheating temperature and decreasing reduction ratio per pass and Ca content. The UTS and YS were not strongly dependent on the Ca content but the elongation decreased with increasing Ca content. The decrease of elongation in Ca containing alloys was least when the sheets were fabricated under preheating temperature of $400^{\circ}C$ and reduction ratio per pass of $15\%$. The sheets had the sound external features with little side cracks by homogenization of gravity cast AZ31-xCa alloys before hot rolling. In the cases of AZ31-xCa alloys containing under $1wt.\%$ Ca, the annealed sheets after homogenization and hot rolling had the similar tensile properties to those of AZ31 sheet.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.118-121
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• 2005

The square cup drawing of magnesium alloy AZ31 $(aluminum\;3\%,\;Zinc\;1\%)$ sheets was studied by experimental approach in various temperatures (200, 250, 300, 350, $400^{\circ}C$) when blank holding force (BHF) was controlled in real-time. And so on, the drawability was measured with the different die and punch coating. The square cup drawing test was performed by three different coated punches (CrN, TiCN, Non-coated). BHF was set about 2.0 KN, forming speed was 50 mm/min, blank thickness were 0.5, 1.0mm and the cup size was 40 mm by 60 mm after forming. The experimental data of square cup drawing test show that the tools coating and temperature were effect on the drawbility.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.395-398
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• 2009

The purpose of this paper is to investigate the effect of annealing treatment on cold formability of magnesium alloy sheet AZ31. The AZ31 sheets with three different thickness (1.0t, 1.6t, 2.0t) were annealed at three different temperatures ($345^{\circ}C$, $400^{\circ}C$ and $450^{\circ}C$). The mechanical properties and microstructure evolution of the annealed AZ31 were examined as well as limit dome height (LDH) and compared with those of as received one. The cold formability was enhanced but the strength was deteriorated by the annealing treatment.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.378-381
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• 2009

In this study, the repetitive loading-unloading tensile tests with AZ31B magnesium sheet metal have been conducted under various elevated temperatures to check out how the Young's moduli of the sheets evolve during the plastic deformation. The loading-unloading tests have been carried out at every 1% of strain increment. With the tested results, some damage parameters of magnesium sheets based on the Lemaitre's continuum damage theory could be calculated at room temperature, $100^{\circ}C$, $150^{\circ}C$, $200^{\circ}C$ and $250^{\circ}C$. It has been shown that the critical damage parameters obtained in all temperature conditions are within the range of 0.12 to 0.18.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.66-70
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• 2008

In this study, the formability of AZ31B magnesium alloy sheets was investigated by the analytical and experimental approaches. Tensile tests and limit dome height tests were rallied out at several temperatures between $25^{\circ}C$ and $300^{\circ}C$ to obtain the mechanical properties and forming limit diagram (FLD). The FLD-based criterion considering the strain-path and the blank temperature was used to predict the forming limit in a deep-drawing process of cross-shaped cup by finite element analysis. This criterion proved to be very useful in determining the optimal process conditions such as blank shape, punch velocity, minimum comer radius, fillet size, and so on, through the comparison between FEA and experimental data. In particular, the temperature of each tool that provided the best formability of the blank was determined by coupled temperature-deformation analyses. A practical method that can greatly reduce the forming time by increasing the punch speed during the forming process was suggested.

• Transactions of Materials Processing
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• v.14 no.7 s.79
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• pp.635-641
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• 2005

The crystal structure of magnesium was hexagonal close-packed (HCP), so its formability was poor at room temperature. But formability was improved in high temperature with increasing of the slip planes. Purpose of this paper was to know about the mechanical properties of magnesium alloy (AZ31B), before warm and hot forming process. The mechanical properties were defined by the tension and compression tests in various temperature and strain-rate. As the temperature was increased, yield·ultimate strength, K-value, work hardening exponent (n) and anisotropy factor (R) were decreased. But strain rate sensitivity (m) was increased. As strain-rate increased, yield·ultimate strength, K-value, and work hardening exponent (n) were increased. Also, microstructures of grains fined away at high strain-rate. These results would be used in simulations and manufacturing factor fer warm and hot forming process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.407-410
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• 2005

The drawability of AZ31B magnesium sheet is estimated according to the variable temperatures (200, 250, 300, 350 and $400^{\circ}C$), forming speed (20, 50, 100 mm/min), thickness (0.8, 1.4 t), blank holding force (1.0, 1.4, 1.7kN). The deep drawing process (DDP) of circular cup is used in forming experiments. The results of deep drawing experiences show that the drawability is well at the range from 250 to $300^{\circ}C$, 50mm/min forming speed and 1.4kN blank holding force. The 0.8t magnesium sheets were deformed better than 1.4t. BHF was controlled in order to improve drawability and protect the change of cup thickness. When BHF was controlled, tearing and thickness change were decreased and LDR. was improved from 2.1 to 3.0.

• Laser Solutions
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• v.14 no.3
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• pp.12-16
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• 2011

In automotive industry, because of the consideration of fuel economy, lightweight alloys have been adopted and are expected to be extensively used in the future. Magnesium alloys are among the promising materials, due to their lightweight and good mechanical properties. This study is related to the laser weldability of AZ31B magnesium alloy, an all-purpose wrought alloy with good strength and ductility. A 4kW Nd:YAG laser was used to join AZ31B sheet, and the effects of welding parameter on the quality of lap-welded joints were investigated. As a result of this study, the optimal condition was obtained, and the effect of gap distance was also revealed on the porosity control.