Huachan Fang

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 Yb additions on microstructures and properties of 7A60 aluminum alloy

Abstract Al-Zn-Mg-Cu-Zr alloys containing Yb were prepared by cast metallurgy. Effect of 0.30% Yb additions on the microstructure and properties of 7A60 aluminum alloys with T6 and T77 aging treatments was investigated by TEM, optical microscopy, hardness and electric conductivity measurement, tensile test and stress corrosion cracking test. The results show that the Yb additions to high strength Al-Zn-Mg-Cu-Zr aluminum alloys can produce fine coherent dispersoids. Those dispersoids can strongly pin dislocation and subgrain boundaries, which can significantly retard the recrystallization by inhibiting the nucleation of recrystallization and the growth of subgrains and keeping low-angle subgrain boundaries. Yb additions can obviously enhance the resistance to stress corrosion cracking and the fracture toughness property, and mildly increase the strength and ductility with T6 and T77 treatments.

Effect of Yb addition on strength and fracture toughness of Al-Zn-Mg-Cu-Zr aluminum alloy

The effect of Yb addition on the strength and fracture toughness of Al-Zn-Mg-Cu-Zr aluminum alloy was investigated by measuring tensile properties and fracture toughness. The surface morphology was observed by optical microscopy, scanning electron microscopy and transmission electron microscopy. The results show that Yb addition can produce fine coherent Yb contained dispersoids. Those dispersoids trend to inhibit Al matrix recrystallization and retain the recovery deformed microstructure. Compared with Al-Zn-Mg-Cu-Zr alloy, Yb contained alloy demonstrates mechanical property improvements from 710 MPa to 747 MPa for ultimate strength, from 684 MPa to 725 MPa for yield strength, from 21 MPa•m(superscript 1/2) to 29 MPa•m(superscript 1/2) for fracture toughness with T6 treatment.

Effect of Yb Additions on Microstructures and Properties of High Strength Al-Zn-Mg-Cu-Zr Alloys

The effect of 0.30 Yb (mass fraction,%) additions on the microstructure and properties of high strength Al-Zn-Mg-Cu-Zr aluminum alloys has been investigated by TEM, optical microscopy, hardness and electric conductivity measurement, tensile test, stress corrosion cracking test. The results show that the ytterbium additions to high strength Al-Zn-Mg-Cu-Zr aluminum alloys significantly inhibited recrystallization during solution treatment. The tensile and yield strengths, elongation, hardness, electric conductivity and stress corrosion cracking resistance of the Yb-containing alloys are improved compared to the alloys without Yb additions. By Yb additions, the critical stress intensity (KISCC) is enhanced from 7 MPa·m1/2 up to 14.5 MPa·m1/2 with the improvement of the strength and ductility. The mechanism for the property improvement from Yb additions has been discussed.

Microstructures, mechanical and oxidation behaviors of C/C composites modified by NiAl alloy

Abstract Carbon/carbon composites modified by NiAl alloy were prepared using vacuum reactive melt infiltration methods with NiAl and titanium mixed powders as raw materials. The microstructures were investigated by scanning electron microscopy. The fracture behavior, infiltration and oxidation mechanism were further discussed. The results indicated that NiAl alloy exhibited good wettability on the C/C preform because a TiC reaction layer formed at the interface. Multi-layer (PyC/TiC/NiAl+TiC) coating evenly and compactly distributed on the surface of the carbon fiber in tubular form. The penetration depth of molten NiAl alloys depended on the reaction between the PyC and titanium. The impact fracture was inclined to along the interface between the NiAl permeability layer and C/C matrix. Al 2 TiO 5 and TiO 2 formed on the surface, while the interior multi-layer tubular structure partially remained after oxidation at 1773 K for 30 min.

Influence of FeCrAl fiber on microstructure and mechanical properties of FeCrAl(f)/HA composites

Abstract FeCrAl fiber-reinforced hydroxyapatite (HA) biocomposites (FeCrAl(f)/HA) were fabricated by the hot pressing technique. The metallographic microscopy, X-ray diffractometry, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to observe and analyze the microstructure and composition of FeCrAl(f)/HA composites, respectively. The mechanical properties of FeCrAl(f)/HA composites were measured by the three-point-bending test. The results show that the composite can be reinforced by FeCrAl fiber and enhanced gradually, and then declined with the increase of the content of FeCrAl fiber (0-11%, volume fraction) in the whole range of experiments. Both the HA matrix and FeCrAl fiber integrate very tightly and bit into each other very deeply and counter-diffusion takes place to some extent at two-phase interface. The optimum parameters of FeCrAl(f)/HA composite are diameter of 22 μm, length of 1–2 mm and of volume faction of about 7% for FeCrAl fibers.