SIMA Process Research Articles

Effect of Multidirectional Forging and SIMA Process on Mechanical and Tribological Behavior of Hypereutectic Al-18 Wt.% Si Alloy

Effect of Multidirectional Forging and SIMA Process on Mechanical and Tribological Behavior of Hypereutectic Al-18 Wt.% Si Alloy

Characterization, fate and impact of ISB products from different types of crude oils: Literature review and experimental study for ISB predictive modelling and SIMA process

In situ burning (ISB) is an OSR (Oil Spill Response) technique generally not accepted as a “standard” response by most regulators. Main reluctance generally comes from the occurrence of large and dark smokes plumes as well as possible heavy burn residues likely to sink and reach the seafloor. However, ISB has been widely used during the Macondo oil spill in 2010 and highlighted as a promising operational technique. Additionally, standard OSR modeling tools do not consider ISB, as there is a lack of knowledge in the capacity to predict accurately the physico-chemical characteristics, fate and ecotoxicity, of the burn products from large varieties of crude oils. In order to provide dispassionate arguments, we have conducted a study to gain knowledge and try to develop predictive capabilities to infer composition and fate of burn products from characteristics of starting crude oils. The study comprises both large literature review and experimental work where six crude oils of different types (along with corresponding weathered oils) were burnt, and all products quantified and analyzed (physico-chemistry), at both laboratory scale (burning bench) and pilot scale (fire platform). Additionally, ecotoxicity testing on Vibrio fischeri bacteria and Phaeodactylum tricornutum algae were conducted on crude and weathered oils, burn residues, water and soot. The fate of burn residues was also investigated through dispersibility, emulsification and biodegradability testing. The experimental work led to a very large set of data which was subject to multivariate regression statistical treatments to build predictive models. Main data investigated were burn efficiency, density, viscosity, SARA (Saturates, Aromatics, Resins, Asphaltenes) composition, n-alkanes and PAHs (polycyclic aromatic hydrocarbons) distributions in burn residues, gas emissions composition, soot' PAHs distribution in the smokes, and ecotoxicity data of burn residues, soot and water. The paper describes the main results of this study, with promising outcomes to develop predictive ISB modeling and help addressing objectively the relative impact of ISB within the SIMA process in comparison with other cleaning responses.

Processing and characterisation of modified strain-induced melt activation processed Al–Si alloys

In the present study, the microstructural features and its correlation with mechanical properties of modified strain-induced melt activation (modified SIMA) processed Al- (7, 12, 14 wt-%) Si alloys are investigated. The microstructure of modified SIMA process Al–Si alloys consists of globular α-Al grains, primary Si particles and Al–Si eutectic phase. The casting defects and surface roughness are minimised and the morphology of eutectic silicon is modified after modified SIMA treatment. The mechanical properties of modified SIMA processed samples are increased significantly as compare to as-cast alloy due to reduction of porosity, formation of fine globular microstructu+re and accumulation of high dislocation tangle near primary Si particles.

Microstructural and Mechanical Evolution of Semisolid 7075 Al Alloy Produced by SIMA Process at Various Heat Treatment Parameters

A homogeneous equiaxed grain structure is necessary for semisolid forming of aluminum alloys. One of the methods used to obtain such microstructure is strain induced melt activated process. The aim of this work is to optimize the heat treatment parameters for extruded 7075 alloy required to obtain the spheroidal grain structure suitable for thixoforging. For this purpose, 7075 was subjected to isothermal heat treatment at two different temperatures, 620 and 630 $${^{\circ }}$$ C for 5, 10, 15, 20, 25, 30, 35 and 40 min. Optical microscopy analysis and mechanical tests were carried out to characterize the effects of different isothermal heat treatment parameters. Optimal heat treatment parameters were determined by the change in mechanical properties and microstructure. It was found that at 630 $${^{\circ }}$$ C for 25 min resulted in 564 MPa yield stress, 616 MPa tensile stress and 5.3% elongation as the highest values in the experimental work carried out in this study.

Finite element analysis of stress–strain localization and distribution in Al-4.5Cu-2Mg alloy

Abstract Finite element analysis has been carried out to understand the effect of various processing routes and condition on the microscale deformation behavior of Al-4.5Cu-2Mg alloy. The alloy has been developed through four different routes and condition, i.e. conventional gravity casting with and without refiner, rheocasting and SIMA process. The optical microstructures of the alloy have been used to develop representative volume elements (RVEs). Two different boundary conditions have been employed to simulate the deformation behavior of the alloy under uniaxial loading. Finally, the simulated stress–strain behavior of the alloy is compared with the experimental result. It is found that the microstructural morphology has a significant impact on stress and strain distribution and load carrying capacity. The eutectic phase always carries a higher load than the α(Al) phase. The globular α(Al) grains with thinner and uniformly distributed eutectic network provide a better stress and strain distribution. Owing to this, SIMA processed alloy has better stress and strain distribution than other processes. Finally, the simulated yield strength of the alloy is verified by experiment and they have great agreement.

Effects of pre-deformation on microstructure and tensile properties of Al—Zn—Mg—Cu alloy produced by modified strain induced melt activation

The effects of Al—8B grain refiner on microstructure and tensile properties of an Al—12Zn—3Mg—2.5Cu alloy produced by modified strain induced melt activation process were investigated. Pre-deformation of 60% was used by hot working at 300 °C. After pre-deformation, the samples were heated to a temperature above the solidus and below the liquidus point and maintained in the isothermal conditions at three different temperatures (500, 550 and 590 °C) for varying time (10, 20 and 40 min). It was observed that strain induced melt activation has caused the globular morphology of α(Al) grains. Microstructural study was carried out on the alloy by using optical microscope and scanning electron microscope in both unrefined and B-refined conditions. The results showed that for the desired microstructures of the alloy during SIMA process, the optimum temperature and time are 550 °C and 10 min, respectively. After the T6 heat treatment, the average tensile strengths increased from 278 to 585 MPa and 252 to 560 MPa for samples refined with 3.75% Al—8B before and after SIMA process, respectively. The ultimate strength of SIMA specimens is lower than that of B-refined specimens.

Microstructure and texture characterization of 7075 Al alloy during the SIMA process

The effect of SIMA process parameters on the crystallographic texture and microstructure of 7075 aluminum alloy was investigated. Specimens of 7075 were subjected to 10–55% uniaxial compression strain at ambient temperature and then semi-solid treatment was carried out at a range of 600 to 620°C for 5–35min. The fiber textures of <110>║CD and <111>║CD were dominant textures in compressed samples. The textures were transformed to a randomized texture following the formation of equiaxed and globular grains. Intense segregation of Cu and Si and appreciable depletion of Mg were observed at grain boundaries during soaking time. The grain boundary composition approaches Al–Cu and Al–Si binary eutectics, which facilitates grain boundary melting. Effects of temperature and strain on both the coarsening kinetics of solid particles and the pinning of grain boundary liquid films are also discussed.

Effect of Al-5Ti-1B master alloy and heat treatment conditions on the mechanical properties and dry sliding wear behavior of an Al–Zn–Mg–Cu aluminum alloy produced by SIMA process

In this study, the effect of Al–5Ti–1B grain refiners and modified SIMA process on an Al–Zn–Mg–Cu alloy was studied. The optimum level of Ti was found to be 0.1wt.%. The specimens subjected to deformation ratio of 40% (at 300°C) and various heat treatment times (10–40min) and temperature (550–600°C) regimes were characterized in this study. Reheating condition to obtain a fine globular microstructure was optimized. Microstructural examinations were conducted by optical and scanning electron microscopy coupled with an energy dispersive spectrometry. The optimum temperature and time in SIMA process are 575°C and 20min, respectively. T6 heat treatment including quenching to room temperature and aging at 120°C for 24h was employed to reach to the maximum strength. Significant improvements in mechanical properties were obtained with the addition of grain refiner combined with T6 heat treatment. After the T6 heat treatment, the average tensile strength increased from 283MPa to 587 and 252MPa to 564 for samples refined with 2wt.% Al–5Ti–1B before and after SIMA process, respectively. The results showed that ultimate strength of globular microstructure specimens was a lower value than that of Ti-refined specimens without SIMA process.

Microstructural evolution of A356.2 alloy prepared by the SIMA process

Abstract Cross wedge rolling is introduced into the strain induced melt activation process before cold compression to prepare semisolid A356.2 alloy. The microstructural evolution of semisolid A356.2 alloy under as-rolled and as-deformed conditions has been investigated. The results show that the microstructure of as-rolled A356.2 alloy after partial remelting consists of predominantly elongated and aggregated solid particles along the rolling direction. Higher compression deformation for as-deformed A356.2 alloy can result in finer solid particles distributed in the liquid matrix and improve spheroidization of these particles. After the solid particles are separated into finer ones due to liquid penetration, Ostwald ripening plays the key role in particle coarsening. The current coarsening rate constant is 412 μm 3 s − 1 at 580 °C.

An investigation on the microstructural evolution and mechanical properties of A380 aluminum alloy during SIMA process

Microstructural evolution and tensile properties of thixoformed near net shape parts of A380 aluminum alloy have been studied. The effect of plastic deformation and holding time in the appropriate semi-solid temperature has been investigated in the strain-induced melt activating process (SIMA). The results of image analysis showed that by increasing the deformation value from 5% to 11%, the recrystallized α-Al grains gradually refined as a result of the increasing the nucleation rate. At the value of 11% plastic deformation a dominant globular structure of α-Al grains was obtained. However, further increasing in the plastic deformation (14%) reduced considerably the shape factor. The equivalent diameter and the shape factor of the globular grains were 70.3 μm and 79%, respectively, after about 11% of plastic deformation. Holding time of the specimens at the semi-solid temperature has been studied from zero to 30 min. It was found that the holding time of 25 min is the best to prevent grain growth. The mechanical properties of thixoformed alloys were also investigated. The results showed that the yield, tensile strength and elongation have been increased considerably using thixoforming, compared with the as-cast condition.

Evolution of the semi-solid microstructure of ADC12 alloy in a modified SIMA process

Abstract Semi-solid metal processing is a new developing technology. This processing has a more advanced technology than traditional ones such as forming and casting. The quasi-spherical grain has been formed by recrystallization of the dendrites during reheating in semi-solid state. The strain-induced melt activation is simple and does not need expensive equipment for preparing semi-solid billets. In this paper a modified method was proposed based on the strain-induced melt activation process. The microstructure and mechanical properties of ADC12 aluminum alloys prepared by the modified strain-induced melt activation process were studied. Different levels of heating temperatures and holding times were used in this investigation. The results of heating experiment revealed that the optimum heating temperature, isothermal holding time and average size of particles were 828 K, 1800 s and 70 μm, respectively. The results of isothermal treatment showed that the size of spherical particles increased linearly with extending the holding time at the 828 K. In the meantime the quantity of particles showed the parabola descent. These phenomena are in accordance with the Lifshitz–Slyozov–Wagner theory and Ostwald ripening.

The Effects of Isothermal Temperature on the Microstructure of Semisolid A6070 Alloy Produced by SIMA Process

The effects of isothermal temperature on the microstructure evolution of semisolid A6070 alloy produced by strain-induced melt activation process were investigated. The results showed that high semisolid isothermal temperature could make the semisolid particles more globular, but the size of the particles would grow larger and accelerate the spherical evolution of the solid particles. It was found that the optimal process temperature should be 620 °C and 10 min of isothermal temperature based on the conditions of this paper.

Effect of RE elements on the microstructural evolution of as cast and SIMA processed Mg–4Al alloy

In the present article, the effect of Rare Earth elements on the microstructural development of as cast and semisolid Mg–4Al alloy produced by SIMA process is studied. Investigation conducted by metallographic observation, scanning electron microscope and quantitative metallographic methods. Results showed that alloy's dendrites turn into larger fully dendritic shape with sharp and narrow arms from equiaxed rosette type as the amount of RE elements increased from 0 through 4%. The effect of RE elements on the microstructure of the treated-alloys was detectable through elimination of vast number of intragranular liquid droplets as well as by decreasing kinetic of microstructural changes. It was shown that the trend of grain coarsening decreased drastically by addition of RE elements to the Mg–4Al alloy during partial remelting at 610 °C. Moreover, the effect of REs on the other parameters such as fraction of liquid, shape factor and particle size was studied.

The effect of rare earth elements on the kinetics of the isothermal coarsening of the globular solid phase in semisolid AZ91 alloy produced via SIMA process

In the present study, the effects of rare earth (RE) elements on the microstructure and coarsening kinetics of the solid globular particle in the semisolid slurry of AZ91 magnesium alloy have been studied at 570 °C and 580 °C. The results showed that the coarsening kinetics of the solid globular particles in semisolid slurry of AZ91 alloy satisfies the Ostwald ripening theory. It was shown that the coarsening rate of the solid particles decreases by adding RE elements into AZ91 alloy, specially at 580 °C, which results in the smaller particles size. It was attributed to the solid–liquid interfacial energy reduction due to the addition of RE elements.

Study of Microstructural Evolution and Phase’s Morphology after Partial Remelting in A356 Alloy

In this work, effective parameters of SIMA process to obtain non dendritic microstructure in A356 alloy were investigated. In addition, the effect of SIMA process on the evolution of morphology of silicon and intermetallic phases in this alloy was studied. Microstructure images obtained from optical microscopy and SEM observation showed that increase in plastic work up to 40% and then holding of samples in the semi solid state at temperature of 580oC, causes that primary dendritic structure changes to non dendritic, fine and globular structure, but optimum reheating time completely depended on initial thickness of samples. If all parameters of SIMA process are the same, the grain boundaries of thinner samples begin to wet and following globalization will be completed in shorter reheating time rather than thicker ones. Moreover, it was found that the intermetallic phases lost their angular or needle morphology and gradually changed to rounded morphology and even to globular form. Also the optimum reheating time thoroughly depends on primary casting microstructure as the finer casting microstructure begin to globalize faster than thicker one under more little stains.

Effect of predeformation manner on semi-solid structure of AZ61 magnesium alloy in sima process

The effect of predeformation manner, predeformation ratio and isothermal heat-treat parameter on the non-dendrite structure of AZ61 magnesium alloy in SIMA process was studied. Under coequal heat-treat condition, the impact of the hot upsetting predeformation on semi-solid microstructure in SIMA process was compared with that of the cold compressive predeformation. The results indicate that non-dendrite microstructure in AZ61 magnesium alloy billets can be obtained by hot or cold upsetting predeformation in SIMA process, although their mechanisms of evolution are different. Increasing hot or cold upsetting predeformation ratio can enhance the effect and quality of the non-dendrite microstructure formed before storage energy up to saturation, but the proper isothermal temperature and holding time should be selected.

Effect of predeformation and heat treatment conditions in the SIMA process on microstructural and mechanical properties of A319 aluminum alloy

Abstract In this study the influences of predeformation and heat treatment conditions on stress-induced melt activating process (SIMA) of A319 aluminum alloy were investigated. At 30% of predeformation a dominant globular structure of grains was obtained. However, further increasing of the predeformation rate considerably reduced the shape factor. The holding time of 10–15 min at semi-solid temperature of 580 °C was suggested in order to prevent grain growth. Coarsening of the grains by excess time or temperature of heat treatment reduced the tensile strength of the alloy.

Evolución microestructural y propiedades reológicas de la aleación AA6063 fabricada mediante técnicas de procesado semisólido (SIMA y MHD)

In this work the rheological behaviour and the microstructural evolution of alloy AA6063 submitted to two different processing routes were studied: cold deformation and partial fusion (SIMA process) and magneto hydrodynamic stirring during its solidification (MHD process). The microstructural evolution during the isothermal holding was studied to verify if the Ostwald ripening mechanisms, classic growth and coalescence, are applicable to alloys made by these processing routes. The rheological properties were evaluated using a compression rheometer with parallel plates and digital capture of position and time data. Compression tests were made in short cylinders extracted from ingots that showed: a dendritic microstructure typical of as cast material, a typical microstructure of cold deformed material and a microstructure of materials obtained by MHD process. It was found that a globular microstructure has a typical behaviour of a fluid when being formed in semisolid state, contrary to the behaviour of the as cast dendritic microstructure. In addition, the mechanisms that operate in the microstructural evolution during the isothermal holdings were verified, through metallographic analysis.

Characterization of Al 7075 alloys after cold working and heating in the semi-solid temperature range

The effects of cold working and heating conditions on the microstructures of 7075 aluminum alloys were investigated in the SIMA process. Swaging was conducted to control the recrystallization structures in the mushy zone. Different levels of cold working, holding temperatures and holding times were used in this investigation. It was found that at least 50% cold working was necessary in order to obtain a uniform and fine microstructures during semi-solid heating. The holding time should be between 2 and 3 min in order to prevent grain growth. The optimum heat treatment conditions for the thixoforged 7075 parts were investigated. The mechanical properties of thixoforged 7075 aluminum alloys were compared with those of conventionally hot forged alloys.