Effect of Variable Rate Non-isothermal Aging on the Microstructure and Properties of Al-Zn-Mg-Cu Alloy

The effect of variable rate nonisothermal aging (VR-NIA) on the properties and microstructure of Al-Zn-Mg-Cu alloy was studied through testing, such as hardness, friction and wear, intergranular corrosion (IGC), electrochemical corrosion and transmission electron microscopy (TEM) observation. The results showed that the comprehensive properties of Al-Zn-Mg-Cu alloy were significantly improved, and the microstructure morphology was well optimized after a new four stage VR-NIA treatment. After the variable speed process of 200–100–160°C, the hardness of the alloy reaches the highest value. The 3D friction and wear topography show that the wear depth of the specimen is the lowest and the wear resistance is the best. The matrix precipitate phase (MPts) had the smallest average size, the highest volume fraction and the strongest precipitation enhancement. When VR-NIA is completed, the intergranular corrosion depth of the H200 specimen is the smallest, the pitting pits are the fewest, and the corrosion rate is the slowest. Grain boundary precipitate phase (GBP) is coarse, the size and distance increase, it is intermittently distributed, and the corrosion does not progress easily. The corrosion resistance of the alloy is improved because of the increase in the width of the precipitate free zone (PFZ).