Characterizing the Effect of Processing Parameters on Temperature Distribution of 7075 Aluminum Alloy Slurry Prepared by Enthalpy Control Process

There is a strong demand for high-strength aluminum alloys such as 7075 aluminum alloy to be applied for rheocasting industry. The overriding challenge for the application of 7075 alloy is that its solid fraction is very sensitive to the variation of temperature in the range of 40% ~ 50% solid fraction, which inevitably narrows down the processing window of slurry preparation for rheocasting process. Therefore, in this work, a novel method to prepare semi-solid slurry of the 7075 alloy, so called Enthalpy Control Process (ECP), has been developed to grapple with this issue. In the method, a medium-frequency electromagnetic field was applied on the outside of slurry preparation crucible to reduce the temperature difference throughout the slurry. The effect of processing parameters, including heating power, heating time, the initial temperature of crucible and melt weight, on the temperature field of the semi-solid slurry was investigated. The results exhibited that although the all the processing parameters had a great influence on the average temperature of the slurry, heating time was the main factor affecting the maximum temperature difference of the slurry. The optimum processing parameters during ECP were found to be heating power of 7.5 KW, the initial temperature of crucible of 30 °C ~ 200 °C and melt weight of 2 kg.

IMPROVEMENT IN HARDNESS AND ELECTROCHEMICAL CORROSION RESISTANCE OF AL-7075 ALLOY BY ARTIFICIAL AGEING

Artificial ageing of Al-7075 alloy was performed in a muffle furnace at different temperatures ranging from 120∘C to 190∘C for 3[Formula: see text]h. The formation of MgZn2 precipitates in the aged alloy was confirmed through the XRD data. The lattice parameter and crystallite size of aluminum were increased with the increase of the ageing temperature. The scanning electron microscopy results validated the precipitates of different shapes and sizes in the aged samples. The number density of the precipitates was found to be maximum at 170∘C. The Vickers hardness of Al-7075 alloy was increased from 125[Formula: see text]HV to 172[Formula: see text]HV with an increase of the ageing temperature from 120∘C to 170∘C and then decreased at 190∘C. The electrochemical tests of the un-aged and aged samples (in 3.5[Formula: see text]wt.% NaCl solution) showed a decrease in the corrosion rate (0.003[Formula: see text]mm/y) and an increase in the corrosion potential ([Formula: see text]137[Formula: see text]mV) of the alloy upon ageing up to 150∘C, indicating improvement in its corrosion resistance.

Microstructure Evaluation on Micro and Nano Slag Particles Reinforced AA7075 Composites

The research work was focused on utilization of solid industrial waste. In order to investigate the properties of Fe-Cr slag particulates strengthened AA7075 composites. In this paper addition of ferrochrome slag particles as reinforcement in AA 7075 alloy processed through stir casting technique. By varying size of ferrochrome slag particles were added to evaluate the size effects in the given alloy matrix. Prepared composites were subjected to heat treatment and evaluated for microstructure analysis. The results show that there is a uniform distribution of particles in the matrix and that there is a strong bond between the matrix and the reinforcement. Grain refinement in the alloy matrix is observed by inducing slag particles. Further nanocomposites show lower grain size values.

Influence of Micro and Nano Particles on Mechanical Behaviour of Slag Reinforced AA7075 Composites

Present studies are based on adding ferrochrome slag as reinforcement in AA 7075 alloy manufactured via the stir casting process. Two different slag particles are chosen; they are 36μm (Micro) and 68 nm (Nano). This was added to evaluate the size effects in the given alloy matrix. The composites were tested for unique microstructural properties and mechanical properties. The results Revealed uniform particle distribution within the matrix and good bonding between the matrix and the reinforcement. Better mechanical properties are obtained for both micro and nanocomposites than base alloy. This is further enhanced by ageing treatments. nanocomposites show superior mechanical properties than either alloy or micro composite. Interestingly, nanocomposite exhibits an increase in strength with good ductility; same is confirmed with fracture studies.

Microstructure and Wear Properties of Al 7075 Alloy Manufactured by Twin-Roll Strip Casting Process

Al 7075 alloy was manufactured using the twin-roll strip casting (TRC) process, and the mechanical and wear properties of the fabricated TRC process were investigated. To compare the properties of the alloy manufactured by TRC, another Al 7075 alloy was fabricated by conventional direct chill (DC) casting as a comparative material. Based on initial microstructure observations, the Al 7075 alloy manufactured by the DC process showed relatively elongated grains compared to the Al 7075 alloy by TRC process. In both alloys, η(MgZn2) phases were present at the grain and grain boundaries. In the Al 7075 alloy manufactured by the DC process, the η(MgZn2) phases were coarse with a size of ~86 nm and were mainly concentrated in the local area. However, the Al 7075 alloy manufactured by TRC had relatively fine η(MgZn2) phases size of ~40 nm, and they were evenly distributed throughout the matrix. When the mechanical properties of the two alloys were compared, the TRC process showed higher hardness and strength properties than the DC process. In room temperature wear test results, the TRC process exhibited lower weight loss and wear rates compared to the DC process at all wear loads. In other words, the TRC process resulted in relatively superior wear resistance properties compared to the conventional DC process. The wear behavior of both alloys changed from abrasive wear to adhesive wear as the wear load increased. However, the TRC process maintained abrasive wear up to higher loads. Based on the above results, a correlation between the microstructure and wear mechanism of the Al 7075 alloy manufactured by TRC is also suggested.

The Corrosion Resistance of Hard Anodised EN AW 7075 T6 Alloy

In this paper, commercially cold-rolled and artificial aged EN AW 7075 T6 alloy has been used. To ensure increased corrosion resistance, surface hardness, scratching resistance, and aesthetic features, this aluminium alloy was subsequently hard anodised and hot-water sealed (AC-A). The hard anodizing and sealing process increased surface hardness up to 304±13 HV 1 from an initial surface hardness of 194±3 HV 1. Also, the microhardness of the anodised layer and bulk material has been documented. Scanning electron microscopy (SEM) was used for microstructure and trapped precipitates investigation in the 42.9±1.4 thick formed anodised layer investigation. The T6 treated (AC) and hard anodised together with sealed (AC-A) EN AW 7075 alloy corrosion properties were evaluated using the anodic potentiodynamic polarisation tests (PPT) in a neutral 2.5% NaCl deaerated solution. The corrosion rate CR (mm/y) decreased approx. 39-times for the hard anodised and sealed EN AW 7075 alloy (AC-A), associated with the shift of the Ecorr (mV) to more positive values, degreased Icorr (µA) and increased Rp (Ohm) values compared to the artificial aged (AC) alloy. Additionally, the pitting was evaluated using laser confocal microscopy, and the pitting coefficient was also calculated.

Using the Instrumented Indentation Technique to Determine Damage in Sintered Metal Matrix Composites after High-Temperature Deformation

The paper shows the applicability of data on the evolution of the elastic modulus measured by the instrumented microindentation technique to the determination of accumulated damage in metal matrix composites (MMCs) under high temperature deformation. A composite with a V95 aluminum alloy matrix (the Russian equivalent of the 7075 alloy) and SiC reinforcing particles is used as the research material. The metal matrix composite was produced by powder technology. The obtained results show that, under macroscopic compression at temperatures ranging between 300 and 500 °C, the V95\10% SiC MMC has the best plasticity at 300 °C. At a deformation temperature of 500 °C, the plastic properties are significantly lower than those at 300 and 400 °C.