Precipitation hardening and intergranular corrosion behavior of novel Al-Mg-Zn(-Cu) alloys

Highlights: • The novel Al-Mg-Zn(-Cu) alloys with (Zn + Cu)/Mg ratio below 1.5 are different from traditional 2000, 5000 and 7000 alloys. • The precipitation hardening of T-Mg₃₂(AlX)₄₉ phase is the main reason to improve the alloy strength. • The IGC resistance of the higher (Zn + Cu)/Mg ratio alloy are mainly depended on the continuity of GBPs. -- Abstract: High-performance aluminum alloys are desired for applications that require lightweight materials, but it is challenging to overcome the tradeoff between their strength and intergranular corrosion resistance. To overcome this tradeoff, we have prepared novel Al–Mg–Zn (-Cu) alloys with highly Zn content combined with Cu addition. The alloys with a (Zn + Cu)/Mg ratio below 1.5 are different from traditional 2000, 5000 and 7000 series aluminium alloys. The results show that the number density and lattice spacing of intragranular precipitates increase, while the precipitate sizes decreases with the increase of (Zn + Cu)/Mg ratio, which is the reason for the increase of the alloy strength. Meanwhile, the intergranular corrosion resistance of the alloys is also enhanced by decreasing the potential between grain boundary precipitates and the Al matrix, especially in alloys with high (Zn + Cu)/Mg ratios. These results provide a new method for obtaining high-strength and corrosion-resistant aluminum alloys.