Jiang-hai You

Effect of Minor Sc and Zr on Microstructure and Mechanical Properties of Al-Zn-Mg-Cu Alloy

A series of Al-8.2Zn-2.1Mg-2.3Cu based as-cast alloys and some plates with thickness of 4mm containing minor Sc and Zr were prepared. The effect of joint addition of minor Sc and Zr on microstructure and mechanical properties of Al-Zn-Mg-Cu alloys were investigated by using OM, SEM with EDS and TEM. The results show that by adding 0.18% Zr (mass fraction) in the cast alloy, the grains can be refined to a certain degree, and by adding 0.18% Sc a little as well. Adding Sc and Zr can generate strong grain refinement effect and obtain a fine equiaxed grain structure, because primary Al3(Sc(subscript x)Zr(subscript 1-x)) precipitation forms in front of the ɑ-Al grains. The microstructure and tensile test results show that 0.18% addition of Zr does not bring higher tensile strength and elongation to the alloy of adding Sc, but a better inhibition to recrystallization. Recrystallization inhibiting effect is the strongest in the alloys with joint addition of Sc and Zr. When the content of Zr is unchanged, the strength and elongation of the alloys increase with increasing Sc addition. The increase of strength and elongation in the alloys is related to the refine grain strengthening, precipitation particles strengthening and substructure strengthening principles.

Effect of Zr content on quench sensitivity of AIZnMgCu alloys

Abstract The effect of Zr content on quench sensitivity of AIZnMgCu alloys was investigated by mechanical properties testing and microstructure observations. The results show that with the increase of Zr the quench sensitivity relative to hardness and strength increases, while that relative to elongation decreases. From hardness and strength viewpoints, the low quench sensitivity is observed for the Zr-free and 0.05% Zr-containing alloys, which is quite quench sensitive from the ductility viewpoint. The largest quench sensitivity relative to hardness and strength is observed for 0.1% Zr-containing alloy, this is mainly due to large amount of high angle grain boundaries and incoherent Al 3 Zr dispersoids caused by recrystallization, which may efficiently promote heterogeneous precipitation during air quenching. More than 0.05% Zr can significantly decrease the quench sensitivity relative to ductility, which can be primarily attributed to recrystallization inhibiting and grain refining effects of Zr.

Influence of cooling rate after homogenization on microstructure and mechanical properties of aluminum alloy 7050

The influence of cooling rate (0.009–220 °C/s) after homogenization on the microstructure and mechanical properties of high strength aluminum alloy 7050 was investigated by tensile testing, optical microscope, X-ray diffraction, scanning electron microscope, and transmission electron microscope. A lower cooling rate after homogenization resulted in lower mechanical properties after aging. The drop in strength was significant when the cooling rate was decreased from 0.5 °C/s to 0.1 °C/s. A lower cooling rate gave rise to a larger amount of remnant S(Al2CuMg) phase and a higher fraction of recrystallization after solution heat treatment. Consequently, the increase in strength after aging due to precipitation hardening and substructure hardening was less significant in the case of slow cooling. This was supposed to be responsible for the lower mechanical properties due to a lower cooling rate after homogenization.

Prediction of Hardness of Aluminum Alloy 7055 by Quench Factor Analysis

The Vickers hardness time-temperature-properties (TTP) curve of aluminum alloy 7055 was evaluated by interrupted quench technique. The critical temperature range of TTP curve was determined from 210 °C to 420 °C with the nose temperature of 355 °C. The hardness decreased rapidly with isothermal duration in the critical temperature range. The hardness of aluminum alloy 7055 was predicted by quench factor analysis using the TTP curve and cooling curves. The predicted hardness agreed reasonably well with the measured results. The influence of time step and summation temperature range on the predicted results was studied. The cooling rate through the critical temperature range had dominant influence on the final hardness of the alloy.

Optimizing Solution Heat Treatment to Improve Mechanical Properties of Al Alloy 7055

The influence of one- and two- stage solution heat treatment on the microstructure and mechanical properties of aluminum alloy 7055 was investigated. The results showed that in the case of one-stage solution heat treatment in the range of 450 °C to 470 °C, the strength increased while the ductility decreased with temperature. Further increasing temperature led to more dissolution of soluble constituents but a large amount of recrystallization, therefore, the strength decreased while ductility increased. The two-stage solution heat treatment, which included first stage of low-temperature-long-duration and second stage of high-temperature-short-duration heating was suggested for improvement of mechanical properties.