Papers by Keyword: Equiaxed Microstructures

Abstract: Recently, a rheocasting process has been interested to produce a structural part for an automobile industry and so the slurry-on-demand process to make the semi-solid slurry having a fine and globular microstructure has been very important to produce a high quality and cost effective part in the rheocasting process. An electromagnetic (EM) stirrer employing for a slurry making process was designed and prepared to induce simultaneously both a circumferential and vertical fluid flow of a melt in order to control a rotation angle of EM stirring of a poured melt. In the present study, the semi-solid slurry of Al-15%Cu alloy was produced in the EM stirrer and its microstructure and the orientation distribution function calculated from the pole figure data was examined in accordance with a various rotation angle of EM stirring between 0˚ (circumferential flow) and 90˚ (vertical flow). The size and morphology of primary α phase was affected with a rotation angle of EM stirring and the finest and the most globular primary α phase could be obtained at a rotation angle of EM stirring of 45˚ and 60˚. Also, due to the EM stirring the tendency to random orientation was appeared. Also, the tendency of random orientation was the most at a rotation angle of 45˚ and 60˚. Therefore, it was considered that the rotation angle of EM stirring of 45˚ and 60˚ was the most effective to induce the non-dendritic growth of primary solid phase of EM stirred Al-Cu alloy.

Abstract: In this study, in order to develop the cast product of Al alloy having a globular microstructure by using the elctromagnetic (EM) stirrer, which was specially designed and manufactured to induce a various fluid flow type of melt during solidification, a morphlogy and size of primary solid phase of the solidifying slurry was investigated with respect to EM stirring condition such as an induced magnetic flux density (MFD) and a frequency of input current. The magnetic flux density of EM stirrer was measured by using a gaussmeter and its distribution and magnetic force within Al melt was simulated in ANSYS program. The induced MFD was increased with decreasing a frequency of input current at the same input voltage due to the increased penetrating depth of magnetic field. But, the magnetic force related directly with a stirring strength of melt was increased with the frequency. Both a roundness and size of primary α phase of Al alloy was decreased with increasing a frequency of input current and MFD within the experimental range. Therefore, the primary α phase was refined and globularized at the higher frequency and MFD.

Abstract: Fretting is a potential degradation mechanism of structural components and equipments exposed to various environments and loading conditions. It is well known that the fatigue life under fretting condition decreases approximately 50-70% compared with that under non-fretting fatigue condition. The specific gravity of titanium alloy is 4.5 which is lighter than steel, however, its specific strength, heat and corrosion resistance are superior to steel. Ti-6Al-4V alloy is a kind of a+b phase titanium alloy, and mechanical properties are changed by alloy elements, shapes and distributions of microstructures. In this study, three different kinds of specimens are prepared under different heat treatments in order to produce different microstructures. Through various kinds of mechanical tests, the following conclusions are observed: 1) The microstructures are observed as equiaxed, bimodal and lamellar microstructures respectively. 2) The elongation percentage is superior for the equiaxed microstructure, and the hardness and tensile strength are superior for the lamellar microstructure. 3) The plain fatigue limit of lamellar structure shows higher value than that of the equiaxed and bimodal structures. 4) The fretting fatigue limit considerably decreases compared with the plain fatigue limit for all materials. 5) The fretting damage of contact surface increases with an increase of cyclic loading amplitude under the constant contact pressure.