Strain Induced Melt Activation 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.

Influence of strain induced melt activation (SIMA) on the morphology of primary phase in steel microstructure

Strain induced melt activation (SIMA) is the mechanism for the formation of the globular microstructure under the controlled working process followed by holding the specimen at a temperature between solidus & liquidus pertaining to the given alloy system. The effect of SIMA process on the microstructure of steel, 10% and 15% deformed at 900°C and holding at 1400°C for 3 and 5 min separately were investigated. The metallographic examination of the SIMA processed steel was done and compared with the as received steel. It was observed that SIMA processed steel shows the globular structure as compared with the unprocessed steel. It was also found that as the deformation percentage increases, more globular structure forms. Due to the globular microstructure, there is enhancement in the mechanical properties such as tensile strength and hardness. The parameter such as degree of warm working process, temperature and holding time are important factor in controlling SIMA process. During mechanical working in the SIMA process, strain energy gets stored in the material. The 15% deformation with 3 min holding time enhanced the hardness and ultimate tensile strength by approximately 8% respectively as compared with as received sample. This acts as a driving force for recrystallization of warm worked steel which resulted in equiaxed grains of primary phase in the microstructure.

The microstructure evolution of Al-5Ce alloy prepared by strain-induced melt activation during semi-solid isothermal treatment process

The coarse grains and rough eutectic microstructure of Al-Ce alloy seriously damage its performance. In this study, Al-5Ce alloys with fine eutectic fibers and bimodal grain distribution were fabricated by strain-induced melt activation (SIMA) process. The results demonstrated that with increasing isothermal temperature and soaking time, the Al11Ce3 phase changes from coarsening to remelting and the α-Al grains size decreases due to decomposition by liquid droplets during the semisolid isothermal treatment. And during the subsequent quenching process, the high cooling rate leads to the solidification of fine α-Al grains and the refinement of eutectic fibers and fiber spacing when the Al concentration exceeds the upper limit of eutectic composition, which forms bimodal grains with fine eutectic fibers.

Evaluation of microstructure and mechanical properties of M-SIMA processed Al–7Si alloy

In this research article, the effect of the strain-induced melt activation (SIMA) process on the microstructure and mechanical properties of the Al–7Si alloy has been investigated. The morphology of α-Al grains is changed from dendritic to fine spherical and flaky type eutectic Si to a fine fibrous eutectic Si after the modified strain-induced melt activation (M-SIMA) process. The intermetallic compounds are refined and distributed uniformly throughout the matrix after the M-SIMA process. The mechanical properties have been improved due to fine spherical grain formation with refined eutectic Si. A high tensile strength (UTS: 204 MPa) with a remarkable improvement in ductility (El: 30%) is achieved after the M-SIMA process at 585°C for 30 min in comparison to the as-cast Al–7Si alloy (UTS: 117 MPa, El: 16%).

Effect of Strain Induced Melt Activation Process on the Microstructure and Mechanical Properties of Al-5Ti-1B Treated Al-7Si Alloy

Effect of Strain Induced Melt Activation Process on the Microstructure and Mechanical Properties of Al-5Ti-1B Treated Al-7Si Alloy

Effect of thixoforming and precipitation hardening on microstructure and mechanical properties of Al-10.5Si–3Cu-0.2Mg alloy produced by strain induced melt activation process

The effects of the thixoforming and the precipitation hardening heat treatment on the microstructure and mechanical properties of Al-10.5Si–3Cu-0.2Mg alloy produced by the strain-induced melt activation (SIMA) process have been investigated. According to previous researches of authors, new introduced alloy has superior mechanical properties in addition to good response to aging process compared with the casting aluminum alloys. The results of the image analysis showed that by increasing the deformation from 10% to 20% and the time of semi-solid heat treatment from 10 to 20 min, the best globular structure of α(Al) grains with the grain size and shape factor of 65 μm and 0.81 were obtained at 15 min for 20% pre-deformation, respectively. The thixoforming process increased the ultimate tensile strength of the alloy about 29%, the yield strength about 37% and the elongation about 6%, compared to the as cast condition. The 20% pre-deformed sample experienced precipitation hardening heat treatment in addition to thixoforming had the best mechanical properties having UTS, YS, elongation and hardness of 423 MPa, 331 MPa, 4.41%, and 144.24 BHN, respectively. Thixoforming plus precipitation hardening is an effective procedure to produce a particular microstructure in Al–Si–Cu–Mg system exhibiting the excellent castability and high mechanical properties.

Effect of compression ratio on microstructure evolution of Mg–10%Al–1%Zn–1%Si alloy prepared by SIMA process

A new Mg–10%Al–1%Zn–1%Si alloy with non-dendritic microstructure was prepared by strain induced melt activation (SIMA) process. The effect of compression ratio on the evolution of semisolid microstructure of the experimental alloy was investigated. The results indicate that the average size of α-Mg grains decreases and spheroidizing tendency becomes more obvious with the compression ratios increasing from 0 to 40%. In addition, the eutectic Mg2Si phase in the Mg–10%Al–1%Zn–1%Si alloy transforms completely from the initial fishbone shape to globular shape by SIMA process. With the increasing of compression ratio, the morphology and average size of Mg2Si phases do not change obviously. The morphology modification mechanism of Mg2Si phase in Mg–10%Al–1%Zn– 1%Si alloy by SIMA process was also studied.

Microstructural evolution of Mg-10Gd-3Y-1Zn-0.4Zr (wt%) alloy prepared by strain-induced melt activation process

The semisolid billets of Mg-10Gd-3Y-1Zn-0.4Zr (wt%) alloy were prepared by the strain-induced melt activation (SIMA) route, and the effects of isothermal heating parameters on the morphology and coarsening kinetics of primary solid grains were studied. It was found that the average grain size increased with the increase of isothermal time while the grain size showed different changing laws with the temperature at different isothermal times. The growth behavior of the primary solid grains was predominantly governed by the Ostwald ripening mechanism, although there is coalescence mechanism in some cases. As the isothermal temperature increased from 550 °C to 590 °C, the coarsening rate constant increased continuously and then declined when the temperature was further increased to 610 °C. Compared with other SIMA processed magnesium alloys, the present alloy showed a significantly lower grain coarsening rate constant due to the inhibiting effect of rare earth (RE) elements on coarsening. This research has provided an insight into the microstructural evolution of Mg-RE alloy under different heating conditions, and will provide valuable information for potential industrial applications.

Study of microstructure and mechanical properties of aluminum 7075 alloy extruded in a semi-solid state

In this paper, the effect of strain-induced melt activation process parameters and the effect of forward extrusion parameters on the semi-solid state in the microstructures and the mechanical properties of aluminum 7075 alloy are investigated. The isothermal holding time, isothermal temperature, and predeformation ratio—which are parameters of strain-induced melt activation method—have been selected at 5–20 min, 590–620 °C and 10%–40% respectively. Also, the extrusion ratio is 68%–89% and the extrusion speed is 0.05–0.5 m/s; the parameters are driven from forward extrusion. Samples at an extrusion ratio of 68%, 75%, and 82% were extruded defectively. Sound products were obtained at an extrusion ratio of 89%. So among these stated parameters, it was derived that the extrusion ratio has the greatest effect on obtaining sound products. At predeformation ratios higher than 30%, the shape factor decreased, and the grain size increased, it was clear that a predeformation ratio higher than 30% is inefficient for the process. The yield and ultimate stress for thixo-extruded samples were higher than for hot extruded samples. As expected, most of the mechanical properties in between sound samples (yield stress of 327 MPa, ultimate stress of 459.5 MPa, and elongation 14%) were related to the sample of finest-grained microstructures. The finest-grained sample (25.85 μm) was achieved at isothermal holding time, isothermal temperature, predeformation ratio, and extrusion rate equal to, 20 min, 590 °C, 30%, 0.2 m/s respectively.

Compression Brazing of SiCp/Al Composite Using a Semisolid Zn-Al-Cu Filler Metal Based on the Strain-Induced Melt Activation Process

The compression brazing of SiCp/Al composite using a semisolid Zn-Al-Cu filler metal based on the strain-induced melt activation process was performed. The as-rolled filler metal was placed between pieces of SiCp/Al composite and heated to the semisolid temperature range for 20 min to spheroidize the solid grains of the filler. Subsequent compression caused the solid grains to compress and slide to the SiCp/Al composite surface. This disrupted the oxide film on the composite surface and promoted interdiffusion between the filler and SiCp/Al composite, forming a metallurgically bonded joint upon cooling. The optimum spherical microstructure of the filler metal was obtained at 392°C, resulting in intense solid grain sliding during compression among the samples considered in this study. A significant disruption of the oxide film was observed at 392°C, and the joint showed shear strength of 105 MPa, reaching 78% of that of the base materials.

The semi-solid microstructural evolution and coarsening kinetics of AZ80-0.2Y-0.15Ca magnesium alloy

The semi-solid billets of the AZ80-0.2Y-0.15Ca magnesium alloy (AZ80M) were fabricated through the strain-induced melt activation (SIMA) process by hot extrusion and then partial remelting. The effects of isothermal temperature and soaking time on the microstructural evolution of the SIMA processed AZ80M in the semi-solid state were analyzed. The results showed that the average grain size (Deq) and the shape factor (SF) of globular grains increased with the increase of the isothermal temperature. However, the value of Deq has visibly declined trend with the isothermal temperature rising to 600 °C. The results of the coarsening kinetics of AZ80M alloy indicated that the coarsening rate (K) increases first and then decreases with the reduction of solid volume fraction (fS) and the critical solid volume fraction (fS0) is 0.5. The coarsening mechanism plays a dominant role in the growth behavior of the solid-grains when fS ≥ 0.5, which can be explained by the modified liquid film migration (MLFM) model. However, the melting mechanism plays a more critical role than coarsening mechanism when fS ≤ 0.5, which can be explained by the liquid film migration (LFM) model. In addition, the SIMA processed AZ80M alloy has a lower coarsening rate than other magnesium alloys, which most likely due to the addition of rare earth elements.

Microstructural evolution and mechanical properties of thixoformed 7075 aluminum alloy prepared by conventional and new modified SIMA processes

Abstract The microstructural evolution during semi-solid processing and thixoformability of a 7075 alloy prepared by conventional and new modified strain induced melt activation (SIMA) processes were comparatively investigated in this paper. The semi-solid slurries were thixoformed at 600 °C, at which temperature the solid fraction was estimated to be 0.8. The coarsening process of the semi-solid samples was described using Lifshitz–Slyozov–Wagner theory and the effect of pre-deformation on the coarsening kinetics of the solid particles was discussed. The coarsening rate constant of the new modified SIMA sample showed a remarkable decrease compared to that of the conventional SIMA sample. Microstructural and mechanical investigations indicated that the sample with a near-equiaxed microstructure deforms through the plastic deformation of solid grains mechanism. However, the sliding of solid grains and flow of liquid incorporating solid grains mechanisms were dominant in the sample with a globular microstructure. Also, it was observed that the yield and ultimate strengths and hardness of the sample prepared by the new modified SIMA process after thixoforming and T6 heat treatment increased by about 15 %, 10 % and 25 % respectively, compared to those of the conventional SIMA sample.

Microstructural Features and Wear Characteristics of Semi-Solid Processed A356 Aluminum Alloy

In the present study the microstructural features and tribological characteristics of hot forged A356 Al alloy subjected to SIMA (Strain induced melt activation) and T6 heat treatment (semi-solid) processes have been investigated. The SIMA process consists of hot forging of alloy at 325˚C followed by cold forging at room temperature, isothermal holding at 580˚C for 10 min and quenching. In case of T6 heat treatment, the hot forged alloy was solution treated at 540˚C for 4 hours followed by quenching in cold water and artificial aging at 155˚C for 3 hours. The microstructure of the alloy exhibited a spherical or globular morphology of the primary α-phase with uniform distribution of solutes in the interdendritic region. A detailed analysis of the solidification behaviour of the melt from semi-solid region of the alloy is reported. The reasons for the consequential changes in tribological properties of A356 Al alloy processed by SIMA andT6 heat treatment have been clearly brought out.

Microstructure and mechanical properties of Al-Si alloys processed by strain induced melt activation

Semi-solid metal processing (SSMP) is an effective near net shape forming processes that have many advantages over the conventional metal casting process. The strain induced melt activation (SIMA), one of the SSM processes, is adapted to produce Al-Si alloys with near globular microstructure. Among the cast alloys, Al-Si alloys are widely used in automotive applications owing to their high wear resistance, moderate strength to weight ratio and low thermal expansion coefficient. Conventionally cast Al-Si alloys have dendritic structure and contain defects such as porosity, blow holes, shrinkage etc. To overcome this defect, semi-solid metal processing is used to obtain globular structure with enhanced mechanical properties.In this investigation, the effects of silicon percentage on mechanical properties and microstructure of Al-Si alloys produced through SIMA process was investigated. Al-Si alloys containing 7%, 12% and 14% wt% Si were prepared through melting and casting route. The microstructure and mechanical properties of conventionally cast and modified SIMA processed Al-Si alloys were observed and evaluated. The SIMA processed samples show significantly higher properties than the samples prepared through conventional cast route. The UTS increased but percentage of elongation decreased with increasing Si wt %. The better combination of mechanical properties obtained when 60% deformed Al-7wt%Si alloy was isothermally hold at temperature 585°C for 30 min.

A study on effects of a new two-step strain induced melt activation process on characteristics of Al 7075 alloy

Abstract It is well-known that the strain induced melt activation process results in a globular microstructure which improves the hardness and the ultimate tensile stress. However, its disadvantage is degrading some other properties such as elongation and formability due to the presence of continuous and brittle intermetallic compounds along with the formation of eutectic structures at grain boundaries. Hence, the aim of this research is to introduce a new process called two-step strain induced melt activation to overcome these drawbacks and to improve the microstructure and the formability of Al 7075 alloy. This new process yielded a globular structure and modified the microstructure. Also, the resultant precipitates were discontinuous with a more homogeneous distribution and the eutectic mixture was eliminated. Moreover, the alloy formability and the hardness were effectively enhanced by performing a rolling process.

Microstructure and Tribological Characteristics of Strain-Induced Melt Activation (SIMA)-Processed Al–10Cu–Fe alloy

In the present study, the influence of synthesis methods, namely the conventional metal mould casting (MMC) and strain-induced melt activation (SIMA) processes, on the microstructure and tribological characteristics of Al–10Cu–Fe alloy has been studied. The alloy was prepared by melting the commercial purity aluminium and copper. The effect of holding time in semi-solid region on the microstructure of the alloy subjected to SIMA was studied. Microstructural characterization was performed using optical and scanning electron microscopy, while chemical segregation is investigated using energy-dispersive spectroscopy. Hardness and strength of the resulting alloy are measured using macroindentation and tensile testing, respectively. Near-spherical grains were achieved in the SIMA process with an average grain diameter varying from 44 to 67 µm for holding times ranging from 30 to 55 min. The wear properties of stirred MMC alloy which was subjected to SIMA process are considerably better than those of either conventional MMCs or unstirred MMC subjected to SIMA process. The 50% pre-deformation followed by intercritical annealing at 580 °C and 30 min holding time is the optimum parameters to obtain the wear properties of Al–10Cu–Fe alloy. The improved wear and mechanical properties of the alloy are discussed in the light of the microstructural features of SIMA-processed alloy and the nature of the worn surfaces.

Influence of Processing Parameters on Microstructural Evolution and Tensile Properties for 7075 Al Alloy Prepared by an ECAP-Based SIMA Process

A modified strain-induced melt activation (SIMA) process consisting of homogenization, equal-channel angular pressing (ECAP) and subsequent heating to the semisolid temperatures was introduced to prepare the 7075 aluminum alloy with superior thixotropic behaviors. The effects of both the homogenization and the number of ECAP passes, as well as the isothermal temperatures on the microstructural evolution, were investigated. The results indicate that ideal microstructure wherein fine and globular solid grains surrounded by uniform liquid films can be achieved through ECAP deformation–recrystallization mechanism. Increasing the number of ECAP passes accelerates the recrystallization of strained grains, thus reducing the average grain size and improving the grain sphericity. Moreover, higher holding temperatures and prolonged soaking time can improve the growth of the solid grains. Two main coarsening mechanisms, viz. coalescence and Ostwald ripening, contribute to the growth of the solid grains simultaneously and independently. The tensile strength of the 7075 alloys after four-pass ECAP-based SIMA and T6 heat treatment is relatively lower than the as-received billet, while the elongation of SIMA processed samples is much higher than that of as-received ones. Increasing the number of ECAP passes improves the tensile strength for alloys with and without T6 treatment due to the fine grain strengthening mechanism.

Effects of SIMA (Strain Induced Melt Activation) on microstructure and electrochemical behavior of Al-Zn-In sacrificial anodes

The Strain Induced Melt Activation (SIMA) process is one of the semi-solid forming processes for preparation of non-dendritic microstructures. In current work, the effects of SIMA process on microstructure and electrochemical behavior of Al-Zn-In sacrificial anode were studied. The effect of plastic deformation on the semi-solid microstructure of Al-Zn-In alloy is investigated by applying 10–40% uniaxial compression at ambient temperature and semi-solid treatment was carried out in the range of 635–660 °C for 40 min. Investigation of the electrochemical behavior of anode and Tafel polarization test are performed in 3.5 wt% sodium chloride solution. The results indicate that microstructure of the SIMA processed specimens is finer and more spherical than that of the as-received material. The sphericity increases significantly with the increase of the compression ratio from 10 to 30%, but the variation rate of the average grain size increases and the shape factor decreases with more increase of the compression ratio up to 40%. The average size and sphericity of α-Al solid grains increase with the increase of the heat treatment temperature. Electrochemical tests results show that plastic deformation up to 30% following heat treatment at 650 °C increases the anode efficiency. Furthermore, SEM results indicated uniform corrosion under the aforementioned condition.

Modelling and optimization of semi-solid processing of 7075 Al alloy

The new modified strain-induced melt activation (SIMA) process presented by Binesh and Aghaie-Khafri was optimized using a response surface methodology to improve the thixotropic characteristics of semi-solid 7075 alloy. The responses, namely the average grain size and the shape factor, were considered as functions of three independent input variables: effective strain, isothermal holding temperature and time. Mathematical models for the responses were developed using the regression analysis technique, and the adequacy of the models was validated by the analysis of variance method. The calculated results correlated fairly well with the experiments. It was found that all the first- and second-order terms of the independent parameters and the interactive terms of the effective strain and holding time were statistically significant for the responses. In order to simultaneously optimize the responses, the desirable values for the effective strain, holding temperature and time were predicted to be 5.1, 609 °C and 14 min, respectively, when employing the desirability function approach. Based on the optimization results, a significant improvement in the average grain size and shape factor of the semi-solid slurry prepared by the new modified SIMA process was observed.

Thixoforming of semi-solid AZ91D alloy with high solid fraction prepared by the RUE-based SIMA process

In the present study, semi-solid billets of AZ91D magnesium alloy were prepared by employing the repetitive upsetting-extrusion (RUE) based strain induced melt activation (SIMA) process. Thixoforming experiments were performed using semi-solid alloys experiencing various RUE temperatures and semi-solid reheating temperatures. The microstructure characterization and microhardness of the thixoformed products were investigated. Microstructure examination results indicated that semi-solid globular microstructure ensuring good thixotropic filling performance was prepared by applying the RUE-based SIMA method. Thixoformed components with good surface quality were obtained. Compared with the original as-cast alloy, significant grain refinement and microhardness improvement occurred in the thixoformed components. And the mean grain sizes and microhardness values were measured to be in the ranges of 11.81–23.84 μm and Hv80.67–Hv90.65, respectively. By means of further comparison of microstructure and microhardness, the grain coarsening and microhardness reduction of the thixoformed components were verified by elevating the RUE deformation temperature and semi-solid remelting temperature. Furthermore, strengthening mechanisms during thixoforming involving the application of the RUE-based SIMA route were discussed in detail. The results showed that the comprehensive effect of fine grain strengthening, dispersion strengthening, and solid solubility strengthening should be responsible for microhardness improvement.