Solution strengthening and precipitation strengthening in spinodally decomposed Al-Zn-(Cu) alloys

Microstructure evolution and accompanying hardness changes in spinodally decomposed Al-Zn-(Cu) alloys were studied by microstructure observation, X-ray diffraction and hardness measurement. The results show that the strengthening of the alloys mainly comes from the solid solution of alloying atoms, and the precipitation strengthening caused by spinodal decomposition is much less effective. The hardness increment of the AlZn-2Cu alloy caused by solution strengthening is about 1 GPa. The peak HV hardness increment caused by spinodal decomposition in the same alloy is only about 180 MPa. Adding Cu atoms improves the stability of the microstructure in Al-Zn alloy and greatly delays the aging time to reach the peak hardness state caused by spinodal decomposition. Adding 2% copper makes the hardness of the as quenched AlZn alloy be increased by 300 MPa.