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.

Fatigue Behavior of Al 7075-T6 Plates Repaired with Composite Patch under the Effect of Overload

Repair of aeronautical structures by composite patch bonding has shown its effectiveness in several studies during the last few decades. This repair technique leads to a retardation in the propagation of repaired cracks via load bridging across the patch throughout the adhesive layer, interfacing it with the repaired structure. The purpose of this study is to analyze the behavior of patch-repaired cracks present in thin plates made of aluminum alloy 7075-T6 and subjected to a single tensile overload. The sequence of application of overload on the fatigue behavior was also studied. Fatigue tests were conducted on Al 7075-T6 notched specimens where crack growth and number of cycles to failure were monitored for different patching/overload scenarios. A detailed fractographic study was performed on failed specimens to analyze the micromechanical behavior of the crack growth related to each scenario. The obtained results showed that the application of the overload before bonding the patch leads to an almost infinite fatigue life of the repaired plates.

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.

A Through-Process Experimental Approach to Enable Optimization of Cold Sprayed Al 7075 Consolidation Performance

This work employs an example of a through process experiment systematic approach to study the relationship among powder properties, cold spray (CS) processing parameters, and consolidated specimen behavior through a combined effort of characterization methods and computational models. This process will allow for the systematic isolation of variables that can affect powder and CS deposit properties. In this study, Al 7075 powder was used as feedstock to produce a CS coating using industry-standard processing parameters. Techniques such as SEM, EDS, XRD, nanoindentation, and tensile testing were used to characterize the properties of both the feedstock powder and CS deposits. In addition, computational thermodynamic modeling was used to guide the interpretation of microstructural features of the powder and CS specimen. Finally, an additive yield strength model was employed to quantify the strengthening components introduced through the CS process.