Effect of Pre-Aging, Over-Aging and Re-Aging on Exfoliation Corrosion and Electrochemical Corrosion Behavior of Al-Zn-Mg-Cu Alloys

By means of TEM, hardness, conductivity, tensile strength test, fracture toughness test, polarization curve and EIS, the Al-Zn-Mg-Cu alloys treated by a new multi-stage aging system, i.e. pre-aging, over-aging and re-aging (120°C/24h + 160°C/8h + 120°C/24h), were characterized. It is found that compared with the Al-Zn-Mg-Cu alloys treated by T76 (120°C/24h + 160°C/8h), the new multi-stage aging treatment can improve the tensile strength, fracture toughness, hardness and conductivity of the alloys at the same time. This is mainly due to the pre-aging, over-aging and re-aging process of super high strength aluminum alloys. Compared with the two-stage over aging process, the formation of multi-stage multi-phase precipitation structure can improve the strength, toughness and corrosion resistance of the alloys at the same time. The polarization curve is consistent with the conclusion. Therefore, we conducted this study to test how the comprehensive properties of the alloy can be improved.

Effect of Minor Cr Additions on Dispersed Phase and Properties of Al-Zn-Mg-Cu-Zr Alloys

The influences of Cr on dispersed phase and properties of Al-Zn-Mg-Cu-Zr alloys were investigated by mechanical testing, slow strain rate stress corrosion, intergranular corrosion, combined with optical microscope, scanning electronic microscope, transmission electronic microscopy (OM, SEM, TEM). Research shows that: with the increase of element Cr, the recrystallization and grain growth had been inhibited, the strength, toughness and corrosion resistance of the alloy increased first and then decreased;when added 0.1 wt% Cr element, the properties of the alloy are the best. The main reasons of that were as below: when added 0.1 wt% Cr element, (Al,Cr)3(Zr,Yb) appeared, that cohered with the matrix. When added 0.18 wt% Cr element, (Al,Cr)3(Zr,Yb) and Al18Mg3Cr2 had been found, making adverse effects on alloys. This work studied the effect of Cr content on recrystallization and grain growth in order to get a new super high strength aluminum alloy.

Effect of cerium on microstructure,mechanical properties and corrosion properties of Al-Zn-Mg alloy

The effects of trace Ce on the microstructure,mechanical properties and corrosion resistance of Al-Zn-Mg alloy were studied by means of metallographic analysis,scanning electron microscopy(SEM),mechanical tensile test,slow strain rate tensile test,cyclic polarization curve test,electrochemical impedance spectroscopy test and anodic oxidation test.The results show that the addition of trace Ce has little effect on the strength of Al-Zn-Mg alloy,but can significantly improve the corrosion resistance of the alloy;The mechanical properties and corrosion resistance of the alloys decrease significantly with the addition of excessive Ce;the addition of 0.04 wt%Ce can reduce significantly the self-corrosive current density of AlZn-Mg alloy and increase obviously passivation film resistance of the alloy.The stress corrosion sensitivity index decreases from 0.612 to 0.219,which improves the corrosion resistance properties significantly.

Simultaneous increase in remanence and coercivity during grain refining of Nd-Fe-B deformed magnets

To explore the feasibility of deep grain-size refinement in overcoming the problem of traditional B-Htrade-off in bulk permanent magnets,the effect of deformation temperature on the texture strength,grain refining,and magnetic properties of slow-deformed Nd-Fe-B magnets was systematically studied.As a result,strong textures with gradual grain refining from conventionally large size of D=650 nm to small nanoscale size of D=53 nm(Ddenotes the lateral size of the aligned plate-like grains)are observed as the temperature reduces from T=650℃to T=450℃.Moreover,magnetic observations show a simultaneous increase in remanence and coercivity as the grain refines from D=650 nm to D=127 nm.The increase in coercivity results from the grain size refinement as well as the smaller aspect ratio of the plate-like grains,and the increase in remanence results from the improved texture homogeneity.As compared with the D=650 nm magnets,the simultaneous increase in remanence and coercivity leads to optimum enhancements of 57%in coercivity,10%in remanence,and 25%in energy product,which demonstrate the feasibility of near-nano scale grain refinement in overcoming the traditional B-Htrade-off for improved(BH)values.The failure of higher coercivities in the D≤80 nm magnets is closely related with the defect effects of the grain boundaries.Mechanisms explaining the grain refining and texture changing behavior were also discussed.