This study investigated the effects of aging and deep cryogenic treatment applied to Al7075 alloy on hardness and wear behavior. In this context, two different categories were created for the aging process. For the first group, after solutionizing the samples at 520 °C for 2 h, aging was applied at 120 °C for 12 h to reach 177 HV hardness. In the second group, after solutionizing at 520 °C for 2 h, the aging process was applied at 200 °C for 8 h to reach a hardness value of 164 HV. In addition, deep cryogenic treatment (12 h, 24 h, and 36 h at −140 °C) was applied to the samples after the solutionizing and aging processes. The pin-on-disc wear test was carried out according to the ASTM G99 standard in order to examine the effects of the aging and cryogenic processes on wear behavior. The highest wear resistance was obtained with the Al7075 sample aged at 120 °C for 12 h followed by the 12-h deep cryogenic treatment. Hardness values and wear test results showed that the applied cryogenic process had positively affected the wear behavior.
In this study, the effects of coated (TiAlN and TiN) drills and cutting parameters on drilling performance were investigated. Drilling operations were carried out by drilling holes 20 mm deep with 5 mm diameter drills on duplex stainless steel (2205). Three different cutting speeds (15, 20 and 25 m/min) and three different feed rates (0.05, 0.075 and 0.1 mm/min) were used in the experiments. The effects of different drills and cutting parameters on the cutting force and surface roughness are measured. Experiments were made in full factorial and optimum conditions were determined for the values measured by the gray relational analysis method. According to the gray correlation analysis value, it was found that the feed rates on the cutting force and surface roughness had a greater effect than the other factors. In addition, variance analysis (ANOVA) was performed to determine the effects of cutting parameters on cutting force (Fc) and surface roughness (Ra). According to ANOVA results, it is determined that the most effective parameter on Ra is the feed rate and the most effective parameter on the second degree is the cutting speed.
In this study, the effect of austempering heat treatment on the cutting forces and surface roughness was investigated during the processing of vermicular graphite cast irons (VGCI) which are widely used in the automotive industry due to their high strength properties. The samples were austenitized at 900 °C for 90 minutes and then austempered at different temperatures (320 °C and 370 °C) for 60 min, 90 min, and 120 min. Machinability tests were carried out under dry conditions at the CNC machining center with the cutting parameters selected in accordance with ISO 3685. As a result of processing of austempered vermicular graphite cast irons with different characteristics the formed cutting forces, surface roughness, cylindricity, and circularity were measured and compared. At the end of the tests, it turned out that the ausferrite morphology (fine or coarse structure) can to be controlled with the austempering heat treatment as well as cutting forces and surface roughness were optimized, respectively. The best surface roughness value was obtained for the austempering parameters of 370 °C and 120 minutes.
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