Strain Induced Melt Activated Process Research Articles

Effect of strain-induced melt activation process and thixoforming on microstructure and mechanical properties of 319 aluminum alloy

The effect of the thixoforming process on the microstructure and mechanical properties of modified and grain refined 319 aluminum alloy has been investigated. The strain-induced melt activated (SIMA) process has been applied to achieve proper microstructure for semi-solid processing. As-cast 319 aluminum parts have a dendritic microstructure and mostly contain defects such as porosity and shrinkage. The semi-solid treatment process eliminates these defects and is used to obtain a spherical structure with enhanced mechanical properties. Image analysis of the semi-solid treated specimens showed that the best sample had the highest amount of α-Al particle sphericity (0.88) and the lowest average equivalent diameter of α-Al phases (56 µm) under the conditions of 30% of the hot pre-deformation at 560 °C and isothermal holding time of 30 min. The specimens were thixoformed after the SIMA process to generate near-net-shape pieces. The thixoforming process enhanced the hardness of 319 aluminum alloy from 78.1 ± 1.91 HB to 115.6 ± 1.73 HB. Based on the tensile test results, the thixoforming process raised the ultimate tensile strength, yield strength, elongation, and toughness by 30%, 69%, 180.5%, and 189%, respectively, compared to the as-cast state.

Effect of Primary Crystals on Pore Morphology during Semi-Solid Foaming of A2024 Alloys

We investigated pore formation in aluminum foams by controlling primary crystal morphology using three master alloys. The first one was a direct chill cast A2024 (Al-Cu-Mg) alloy (DC-cast alloy). The others were A2024 alloys prepared to possess fine spherical primary crystals. The second alloy was made by applying compressive strain through a Strain-Induced Melt-Activated process alloy (SIMA alloy). The third one was a slope-cast A2024 alloy (slope-cast alloy). Each alloy was heated to either 635 °C (fraction of solid fs = 20%) or 630 °C (fs = 40%). TiH2 powder was added to the alloys as a foaming agent upon heating them to a semi-solid state and they were stirred while being held in the furnace. Subsequently, A2024 alloy foams were obtained via water-cooling. The primary crystals of the DC-cast alloy were coarse and irregular before foaming. After foaming, the size of the primary crystals remained irregular, but also became spherical. The SIMA and slope-cast alloys possessed fine spherical primary crystals before and after foaming. In addition to average-sized pores (macro-pores), small pores were observed inside the cell walls (micro-pores) of each alloy. The formation of macro-pores did not depend on the formation of the primary crystals. Only in the DC-cast alloy did fine micro-pores exist within the primary crystals. The number of micro-pores in the SIMA and slope-cast alloys was one third of that in the DC-cast alloy.

Effect of SIMA Process on Microstructure and Wear Behavior of Al-Mg2Si-3% Ni Composite

The microstructural evolution and wear behavior of Al-Mg2Si-3% Ni in situ composite during strain-induced melt-activated (SIMA) process were investigated in this study. In order to induce strain in samples, they were cold deformed by the compression ratio of 10% reduction. Then, they were isothermally re-heated at 540 °C for 20, 40 and 60 min. It was observed some cracks in primary Mg2Si particles which lead to reduce the size of these particles and distribute more uniformly in matrix. Also, they became more globular after SIMA process. Furthermore, the brittle network of eutectic phase has altered remarkably during this process from flake-like to rod- or dot-like. The wear resistance of specimens improved remarkably after SIMA process. It was found that this improvement can attribute to microstructural changes, especially eutectic Mg2Si phase, because this microstructure can curb the crack nucleation in delamination mechanism and consequently reduces the wear rate.

A metal additive manufacturing method: semi-solid metal extrusion and deposition

Different existing metal additive manufacturing (AM) processes have many shortcomings and a lot of activities are centered on improving the final printed metal product. A new method of metal additive manufacturing has been proposed in this paper. Unlike most of the metal additive manufacturing processes, it does not use metal powder. The proposed method utilizes semi-solid metal (SSM) forming combined with deposition process as used in the most common additive manufacturing process for polymers. SSM forming is a promising near net shape technology with several advantages, such as being a porosity-free product and having reduced shrinkage, controlled microstructure, and excellent mechanical performance. Implementation of this technology in metallic additive manufacturing improves the mechanical properties and cost savings. Complicated time-dependent behavior of SSM makes it a challenging issue to utilize in additive manufacturing. A wire feedstock as a metallic filament was employed for the proposed process. However, some material preparations were necessary to get the desired rheological properties at the deposition head. In this study, the strain-induced melt-activated (SIMA) process was applied on a low-melting-temperature Sn-Pb alloy to obtain the desired globular feedstock microstructure. Then, preconditioned wire was fed in a thixo-extruder, which was designed and built for the proposed method in this research. A semi-melted alloy was deposited on the moving substrate to build a metallic part layer by layer. Various parameters of SIMA and thixo-extrusion processes, including wire thermomechanical cycle, feed rate, solid fraction, nozzle and chamber geometry, and others, were examined experimentally, and a sustainable semi-solid metal extrusion and deposition (SSMED) process was achieved. Finally, an acceptable metallurgical layer bonding was obtained at the interface of the deposited layers, with good mechanical properties of the fabricated parts. The new proposed method seems to have great potentials for metal additive manufacturing parts.

The Effect of Deformation Ratio and Heat Treatment Time on the Microstructure and Mechanical Properties of A356 Aluminium Alloy During SIMA Process

The influence of Strain Induced Melt Activated (SIMA) parameters on the globularization of α-Al and microstructure in A356 aluminium alloy were investigated in the present study. After production of samples using conventional permanent mold casting and cold rolling at various reduction, they were heat treated at 590°C for different holding time to spherodize the microstructure. The results indicated that, the grains became smaller, more spherical and having a homogenous distribution by increasing the deformation ratio. Increasing the holding time in heat treatment results the growth of globular grains. The necessary strain for recrystallization is about 15% and the optimum condition was achieved in the samples were 15% rolled and heat treated for 15 minutes at semi-solid temperature, regarding the maximum shape factor and minimum globular grains size. Further increasing in holding time is responsible for grain growth and hardness decline.

Effect of Rolling-Remelting SIMA Process on Semi-Solid Microstructure of ZCuSn10 Alloy

Semi-solid billet of ZCuSn10 (Wt%: 88.25Cu, 10.48Sn) alloy is prepared by strain induced melt activated (SIMA) method which including rolling and remelting process. Firstly, ZCuSn10 alloy is casted, and rolling samples are cut from ingot casting. Secondly, the rolling samples are two pass or four pass rolled after holding 15 minutes at 450°C, then samples with 10% and 20% pre-deformation degree are obtained. The remelting samples are cut from pre-deformed samples. Lastly, the remelting samples are reheated up to 850°C or 875°C, water quenching after holding for 15 minutes. Then semi-solid microstructure of ZCuSn10 alloy is prepared. The semi-solid microstructure of ZCuSn10 alloy is observed and compared with annealed microstructure and microstructure of ZCuSn10 alloy directly remelted after casting. The results indicate that semi-solid microstructure of ZCuSn10 alloy by rolling-remelting SIMA process is uniform and fine grain, and spheroidization level of solid particle is well. The optimum semi-solid microstructure is obtained when alloy with pre-deformation 20% is remelted at 875°C for 15 minutes, the average grain diameter is about 75.80μm, shape factor is 1.62, and volume fraction of liquid phase reaches about 17.28%. Pre-deformation process plays a crucial role in grain refinement and spheroidization during SIMA process for preparing the semi-solid ZCuSn10 alloy, as pre-deformation degree and remelting temperature increases, volume fraction of liquid phase increases, the solid particles in semi-solid microstructure are smaller and rounder. The main mechanism of SIMA process preparing semi-solid billet of ZCuSn10 alloy is that pre-deformation breaks dendrites and stores energy of deformation into alloy, and promotes dendrites fusing through remelting process. Meanwhile, liquid phase occupies sharp corners of solid particles by Sn element diffusing from liquid phase into α solid phase, so that fine and uniform and globular α solid particles are gained.

Microstructure evolution and semi-solid deformation behavior of an A356 aluminum alloy processed by strain induced melt activated method

The effects of strain induced melt activated (SIMA) process parameters on the microstructure evolution of an A356 aluminum alloy have been investigated. It is concluded that a fine uniform globular microstructure may be obtained through heating the 45% pre-deformed specimen at 615°C for 6min. In addition, a model for microstructure evolution during SIMA process is proposed. This accounts for the mechanisms causing the microstructural changes in two successive steps of pre-deformation and heating. The present work also explores the semi-solid deformation behavior of the experimental alloy possessing different initial microstructures, including cast, rosette-like, globular and coarsened ones. The applied thixoforming process encompasses a set of isothermal hot compression tests in the semi-solid temperature range. The results indicate that the SIMA processed specimen with globular microstructure exhibits the lowest flow resistance during thixoforming process, followed by those with coarsened, rosette-like and cast microstructures. This has been justified considering the governing deformation mechanisms for different thixoformed microstructures.

유도가열에 따른 SKH51의 반응고 미세조직 특성 연구

Semi-solid forming of the high melting point alloys such as steel is a promising near-net shape forming process for decreasing manufacturing costs and increasing the quality of the final products. This paper presents the microstructure characteristics of SKH51 (high speed tool steel) during heating and holding in the mushy zone between <TEX>$1233^{\circ}C$</TEX> and <TEX>$1453^{\circ}C$</TEX>, which has been measured by differential scanning calorimetry (DSC). The results of heating/holding experiments showed that the grain size and the liquid fraction increased gradually with temperature up to <TEX>$1350^{\circ}C$</TEX>. The drastic grain growth occurred at heating above <TEX>$1380^{\circ}C$</TEX>. The strain-induced melt-activated (SIMA) process has been applied to obtain globular grains in the billet materials. Working by mechanical upsetting and successive heating of SKH51 into the temperatures in the mushy zone resulted in globular grains due to recrystallization and partial melting.

Effect of Melt Quality and Quenching Temperature on the Mechanical Properties of SIMA 2024 and 7075

Spherical grains can be obtained by several semisolid processes in aluminium alloys. One of these methods is called Strain Induced Melt Activated (SIMA). In this work, commercially available 2024 and 7075 alloys were subjected SIMA process. First, optimised process parameters were investigated for the homogeneous spherical grain structure. This was followed by solution heat treatment of the parts. For the quenching medium, room temperature and 80°C boiling water was selected. The effect of different quenching temperatures over the mechanical properties was tested. Hardness, tensile and fatigue tests were applied. In addition, reduced pressure test was used to assess alloy quality and the results were compared with the mechanical tests.

Effect of Melt Quality and Quenching Temperature on the Mechanical Properties of SIMA 2024 and 7075

Spherical grains can be obtained by several semisolid processes in aluminium alloys. One of these methods is called Strain Induced Melt Activated (SIMA). In this work, commercially available 2024 and 7075 alloys were subjected SIMA process. First, optimised process parameters were investigated for the homogeneous spherical grain structure. This was followed by solution heat treatment of the parts. For the quenching medium, room temperature and 80°C boiling water was selected. The effect of different quenching temperatures over the mechanical properties was tested. Hardness, tensile and fatigue tests were applied. In addition, reduced pressure test was used to assess alloy quality and the results were compared with the mechanical tests.

Study of ECAP Processing Routes on Semi-Solid Microstructure Evolution of A356 Alloy

Semi- solid (SS) processing technologies provide the production of metal parts with homogeneous, fine and globular – grained microstructure. This is one of the most successful and reliable methods to produce near net shape products exhibiting good mechanical properties. Production of feed stock with non-dendritic and spherical structure is the critical factors in semisolid forming. Among several processes to obtain a globular microstructure, the SIMA (strain induced melt activated) process is simple and advantageous with respect to equipment and eliminating the melting stage before reheating. In this research, Al (A356) has been used and in order to induce strain, ECAP (equal channel angular pressing) method has been applied. ECAP is a method in which a great strain is induced and severe plastic deformation without any changes in cross section area occurs. To induce larger strain, ECAP process was carried out on annealed specimens up to several passes in route A (no rotation of samples around linear axis between each pass) and Bc (90◦ rotation of samples around linear axis between each pass), in ambient temperature. The reheating condition was optimized and the comparison between different routes and number of passes was investigated. The microstructure evolution of deformed and reheated Al (A356) was characterized by SEM (Scanning electron microscopy) and optical microscopy. In addition, the relation between the induced strain with size and shape of particles has been studied.

Grain Refinement of 6061 Al Alloy by the Modified Strain-Induced Melt- Activated(SIMA) Process for Semi-Solid Processing

The dynamic process of fine grain evolution of 6061 aluminum alloy during modified strain-induced, melt-activated (SIMA) process was studied. The modified SIMA process employed casting, two stage homogenization, warm multi-forging, and recrystallization and partial melting (RAP). Multi-forging was carried out at a strain rate of 9x10-3 s-1 to accumulate high strains, with decreasing temperature from 250 to 200 °C. The alloy multi-forged with the accumulated strain of about 12 and RAP at 640 °C for 10 min exhibited the uniform equiaxed recrystallized grain structure. Accordingly, it was evident that multi-forging was very effective on grain refinement and grain size uniformity. The present modified SIMA process was discussed as an alternative thermo-mechanical processing for preparing the alloys with fine grained structure for semi solid processing.

Microstructure evolution of SIMA processed Al2024

In this paper, the strain induced melt activated (SIMA) process of A2024 was investigated systematically in order to provide a basis for semi-solid forming of the alloy. To delete the hydrostatic component of stress, the uniform uniaxial compression process is performed. The relation between the grain size and strain before heating is presented and a microstructure evolution model for SIMA is proposed on the basis of experiment. There include two steps in SIMA process. In the first step of plastic deformation, there are two mechanisms to control the deformation, slip or cross-slip or twinning in grain and grain rotation. The deviatory stress will benefit to slip or cross-slip or twinning in grains, and the hydrostatic stress will benefit to rotation of gain. In the second step of heating, the grain boundary will melt first and the shape of the grains will be globe.

Recrystallization Behavior of 7175 Al Alloy during Modified Strain-Induced Melt-Activated (SIMA) Process

A modified strain-induced, melt-activated (SIMA) process for semi-solid processing of alloys was proposed. In order to examine the applicability and effectiveness of the modified SIMA process, the recrystallized microstructures of a high strength 7175 Al alloy prepared by the modified SIMA processes were macroscopically compared to that of conventional process. The modified SIMA process employed casting, two stage homogenization, warm multi-forging, and recrystallization and partial melting (RAP) instead of the conventional process consisted of casting, hot working, cold working and RAP. For the alloy processed by the conventional SIMA process, the recystallized grain size decreased with increasing the cold rolling reduction ratio up to 20% and then almost unchanged. RAP treatments of the 20% cold rolled alloy at above 600 � C and for longer than 30 min resulted in significant grain growth. In case of the modified SIMA process, the alloy multi-forged with the accumulated strain of about 7 and RAP at 575 � C for 10 min exhibited the uniform equiaxed recrystallized grain structure similar to that of the conventional SIMA process under the optimum conditions. The improved processing efficiency of the modified SIMA process over the conventional one, i.e. removal of hot working and saving of RAP time, is attributed to the enhanced recrystallization kinetics due to a high density of Mg(Zn,Al,Cu)2 precipitates which are formed by two stage homogenization, acting as the preferential recrystallization sites and due to the driving force imposed by relatively large amount of uniform deformation by multi-forging.

Microstructural characteristics of aluminum 2024 by cold working in the SIMA process

Abstract The SSF (semi-solid forging) is compound forging technology to manufacture near net shaped parts. For SSF, it is necessarily required to prepare a workpiece with a globular microstructure. Amongst several processes to obtain a globular microstructure, the SIMA (strain induced melt activated) process is very simple and advantageous with respect to equipment. This paper presents the influence of effective strain on globularization with aluminum 2024 alloy in the stage of cold working by the SIMA process. Upsetting and forward extrusion are tested for the stage of cold working and induction heating for heat treatment is also carried out to obtain a globular microstructure, which is observed with an optical microscope. Finite-element analysis to obtain the effective strain of the workpiece in the stage of cold working is performed with the commercial finite element code, DEFORM.