Micro Alloying (ce, Sn) On Al - Zinc - Mg - Cu Alloy Microstructure And Properties Of Influence

Ultra-high strength Al-Zn-Mg-Cu series alloys are widely used in aerospace for its high strength and low density, but Al-Zn-Mg-Cu alloys are highly susceptible to stress corrosion cracking. In this paper, the effect of microalloying(Ce、Sn) on the micro structure and corrosion behavior has been investigated by transmission electron microscope (TEM), scanning electron microscope (SEM) and electrochemical workstation. The results are summarized as follows:1. The addition of Ce can refine the as-cast grains and the as-cast grain boundary microstructure. Besides, the addition of Ce can delay the dissolution of GP zones during aging and η’ phase may nucleate on these GP zones, thus resulting in finer and denser η’ precipitates. And the PFZs (free precipitate zones) are much finer in the Ce-containing alloy. The suitable addition of Ce can enhance the mechanical properties of Al-Zn-Mg-Cu alloys, but excessive Ce addition can decrease the strength and elongation due to the brittle Al8Cu4Ce particles.2. The addition of Sn can refine the as-cast grain of the Al-Zn-Mg-Cu alloys, increase the peak-aging hardness and delay the time to reach peak-aging state. Besides, lower Mg concentration at grain boundaries and more discontinuous grain boundary precipitates were found in the Sn-containing alloy. The Sn addition can remarkably increase the strength and slightly decrease the elongation of the Al-Zn-Mg-Cu alloy. The strength of the alloy with Sn addition is606MPa, higher than that of Sn-free alloy (586MPa). The elongations of Sn-containing and Sn-free alloys are11.6%,10.8%, respectively.3. The addition of Sn can enhance the resistance to intergranular corrosion and exfoliation corrosion.4. The addition of Sn can enhance the SCC resistance, which is likely due to discontinuous grain boundary precipitates and lower Mg concentration at the grain boundary. The discontinuous grain boundary precipitates would decrease the anode corrosion rate. And the lower Mg concentration at the grain boundary can decrease the hydrogen embrittlement susceptibility due to due to the strong interaction between Mg and H.