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    Effects of Different Heat Treatment Conditions on Fatigue Behavior of AA7075 Alloy
    (Walter De Gruyter Gmbh, 2013) Fakioglu, Avni; Ozyurek, Dursun; Yilmaz, Ramazan
    In this study, the effect of different heat treatment processes applied to AA7075 alloys on the fatigue behavior was examined. The processes applied to AA7075 aluminum included annealing (O), high temperature pre-precipitating (HTPP), artificial aging (T6), retrogression and re-aging (RRA). The annealing heat treatment was performed for 2 hours at 500 degrees C and samples were cooled in the furnace. In the artificial aging (T6) process, after the samples were solution treated for 2 hours at 500 degrees C, they were quenched at room temperature and aged for 24 hours at 120 degrees C. In the retrogression and re-aging process, samples were solution treated for 1 hour at 220 degrees C after the T6 process and then re-aged for 24 hours at 120 degrees C. In the high temperature pre-precipitating, pre-precipitates were formed for 30 minutes at 450 degrees C and then, it was aged for 24 hours at 120 degrees C. All samples were characterized through the scanning electron microscope (SEM + EDS), hardness measurements and X-ray difraction (XRD) techniques. At the end of experimental studies, SEM and EDS examinations XRD results revealed that eta (MgZn2) phase formed in the microstructure following the HTTP, RRA and T6 heat treatment processes. As a result of the fatigue tests, the highest fatigue strength was measured in samples treated with artificial aging (T6), the lowest fatigue strength was measured in the annealed (O) samples.
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    THE EFFECTS OF RETROGRESSION PARAMETERS IN RRA TREATMENT ON TENSILE STRENGTH OF 7075 ALUMINIUM ALLOYS
    (Gazi Univ, Fac Engineering Architecture, 2012) Ozyurek, Dursun; Yilmaz, Ramazan; Kibar, Erkan
    In this study retrogression and re-aging (RRA) treatments has been applied on 7075 aluminium alloys after T6 treatment. The alloys were retrogressed at various temperatures and times in the retrogression stage of RRA treatment. The effects of the parameters mentioned above on tensile strengths and % elongations were investigated. Besides fracture surfaces were examined by scanning electron microscopy (SEM) for determination of the effects of retrogression temperatures and times on fracture mechanism. The alloy retrogressed at 220 degrees C for 60 minutes showed the highest tensile strength values, on the other hand, the lowest elongation values. Strong relationship has been seen between hardness and tensile strength; however, no effective relationship for elongation was available. Retrogression temperatures and times affects on microstructure of the alloys, therefore, it has also great influence on the hardness and tensile strength, elongation and fracture mechanism.
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    THE EFFECTS OF RETROGRESSION PARAMETERS ON HARDNESS AND WEAR BEHAVIOURS OF 7075 ALUMINIUM ALLOYS
    (Gazi Univ, Fac Engineering Architecture, 2012) Yilmaz, Ramazan; Ozyurek, Dursun; Kibar, Erkan
    In this study, retrogression and re-aging (RRA) treatments on 7075 aluminium alloys has been carried out. 7075 aluminium alloys that were already T6 temper applied were retrogressed at the range of 180-260 degrees C for durations between 15-75 minutes and later re-aged in T6 aging condition of 120 degrees C for 24 hours. The effects of retrogression temperature and times on the hardness and wear properties were investigated. Wear tests were carried out by using machine that is for pin on disc technique. Worn surfaces of the samples after tests were also examined by scanning electron microscopy (SEM) for better understanding of wear mechanism. Experimental studies show that retrogression treatments parameters such as temperatures and times have great effects on wear resistance of 7075 aluminium alloys. Close relationship between the hardness and wear resistance values were seen in those alloys. Variations in hardness values were all depend on retrogression temperatures and times. The alloy retrogressed at 220 degrees C for 60 minutes showed the highest hardness values and wear resistance.