Songyi Chen

Influence of dual retrogression and re-aging temper on microstructure, strength and exfoliation corrosion behavior of Al–Zn–Mg–Cu alloy

Abstract Influence of dual retrogression and re-aging (dual-RRA) temper on microstructure, strength and exfoliation corrosion (EC) behavior of Al–Zn–Mg–Cu alloy was investigated by hardness measurements, tensile properties tests, exfoliation corrosion tests, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observation combined energy dispersive X-ray detector (EDX) analysis. Dual-RRA temper maintains the matrix precipitates (MPs) similar to RRA temper, meanwhile obtains∼coarser and sparser grain boundary precipitates (GBPs) as well as higher∼Cu and lower Zn content compared with T76 temper. Therefore, dual-RRA temper not only keeps strength equivalent to the RRA temper but also obtains higher EC resistance than T76 temper.

Effect of quenching rate on microstructure and stress corrosion cracking of 7085 aluminum alloy

The influence of quenching rate on microstructure and stress corrosion cracking (SCC) of 7085 aluminum alloy was investigated by tensile test, slow strain rate test (SSRT), combined with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical test. The results show that with decreasing the quenching rate, the size and inter-particle distance of the grain boundary precipitates as well as precipitation free zone width increase, but the copper content of grain boundary precipitates decreases. The SCC resistance of the samples increases first and then decreases, which is attributed to the copper content, size and distribution of grain boundary precipitates.

Effect of heat treatment on stress corrosion cracking, fracture toughness and strength of 7085 aluminum alloy

Abstract The influences of heat treatment on stress corrosion cracking (SCC), fracture toughness and strength of 7085 aluminum alloy were investigated by slow strain rate testing, Kahn tear testing combined with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the fracture toughness of T74 overaging is increased by 22.9% at the expense of 13.6% strength, and retrogression and reaging (RRA) enhances fracture toughness 14.2% without reducing the strength compared with T6 temper. The fracture toughness of dual-retrogression and reaging (DRRA) is equivalent to that of T74 with an increased strength of 14.6%. The SCC resistance increases in the order: T6

Effect of hot deformation conditions on grain structure and properties of 7085 aluminum alloy

Abstract The influences of deformation conditions on grain structure and properties of 7085 aluminum alloy were investigated by optical microscopy and transmission electron microscopy in combination with tensile and fracture toughness tests. The results show that the volume fraction of dynamic recrystallization increased with the decrease of Zener-Hollomon ( Z ) parameter, and the volume fraction of static recrystallization increased with the increasing of Z parameter. The strength and fracture toughness of the alloy after solution and aging treatment first increased and then decreased with the increase of Z parameter. The microstructure map was established on the basis of microstructure evolution during deformation and solution heat treatment. The optimization deformation conditions were acquired under Z parameters of 1.2 × 10 10 −9.1 × 10 12 .

Effect of initial microstructure on hot workability of 7085 aluminum alloy

Abstract The hot workability of 7085 aluminum alloys with different initial microstructures (as-homogenized and as-solution treated) was studied by isothermal compression tests at the deformation temperature ranging from 300 to 450 °C and the strain rate ranging from 0.0001 to 1 s −1 . The strain rate sensitivity of the alloy was evaluated and used for establishing the power dissipation maps and instability maps on the basis of the flow stress data. The results show that the efficiency of power dissipation for the as-homogenized alloy is lower than that of the as-solution treated alloy. The deformation parameters of the dynamic recrystallization for the as-homogenized and as-solution treated alloy occur at 400 °C, 0.01 s −1 and 450 °C, 0.001 s −1 , respectively. The flow instability region of the as-homogenized alloy is narrower than that of the as-solution treated alloy. These differences of the alloys with two different initial microstructures on the processing maps are mainly related to the dynamic precipitation characteristics.

Intensive melt shearing and calcium concentration effects on grain refinement of commercial purity Mg

Abstract The effects of intensive melt shearing and Ca concentration on grain refinement of commercial purity Mg have been investigated by standard TP-1 casting tests, X-ray diffraction combined with the observation of optical microscope and scanning electron microscope. It was found that, without intensive melt shearing, Ca addition greatly improved grain structure of Mg from columnar grain to equiaxed grain. With Ca concentration increasing from 0.01 to 1 wt. %, the average grain size of the alloy gradually decreased. When intensive melt shearing was applied, the grain structures of the alloy remained equiaxed grain with Ca concentration variation. The average grain size first decreased and then kept invariable with Ca concentration increasing to 1 wt. %. The grain refining mechanism of Ca concentration variable and intensive melt shearing was discussed.

Improved Zr grain refining efficiency for commercial purity Mg via intensive melt shearing

Abstract The low concentration Zr and intensive melt shearing effects on grain refinement of commercial purity Mg has been studied. It was found that the low concentration Zr addition, combined with intensive melt shearing, resulted in a significantly grain refinement. The mechanism of grain refinement on the intensive melt shearing dispersing MgO film into individual MgO particle and enhancing the adsorption of low concentration Zr on the surface of MgO particle was proposed.