الفهرس 
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Abstract
Aluminum alloy 7075 is widely used for aircraft structures ,marine ,automotive and industrial application, due to its high strength to density ratio . It is difficult to obtain a combination of optimal strength and corrosion resistance for this alloy. It appears that corrosion resistance of this alloy is related to type , morphology and the percentage of precipitates. One technique to control the precipitate morphology is known as retrogression and reaging treatment (RRA). RRA is consists of two steps :first retrogression of the 7075-T6 material at an intermediate temperature between the aging temperature and the solutioning temperature, second re-aging of the retrogressed alloy at T6 condition. In percent work ,retrogression treatment at 200oC for 5,10,20,30,40,50,60 minute followed by reaging at 120oC for 24 hr was carried out. Techniques like Optical Microscopy, X ray fluorescence, Energy Dispersive X-ray Spectroscopy and Scanning Electron Microscopy have been used to investigate microstructure and surface morphology after retrogression process and RRA treatments. The material is tested for hardness and electrochemical behaviour after retrogression and RRA treatments. Electrochemical test of AA7075 is studied in through electrochemical techniques Cyclic Potentiodynmic Polarization in 3%NaCl solution. Results show that retrogression and reaging treatment have signification effect on hardness ,corrosion rate, pitting potential and type of attack of 7075 alloy . X-ray diffraction patterns and isothermal quaternary section of Al-Zn-Mg-Cu alloys indicate that the M (Mg Zn2 )and S (Al2Cu Mg )phases are the main precipitates. It was observed that the strength reaches the lowest minimum after 30 min retrogression time. Increase in retrogression time causes increase in hardness but further increase in retrogression time causes the hardness to decrease. Subsequent reaging treatment increases the hardness. Retrogression treatment increase the corrosion resistance of the alloy.