Hai Hao

Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy

Abstract Effects of Nd on microstructure and mechanical properties of as-cast Mg-8Li-3Al alloy were investigated by OM, X-ray diffraction (XRD), EPMA, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that the dendrites sizes of α phase were decreased by the Nd addition. When the amount of addition Nd was 1.6 wt.%, the alloy with the smallest α phase was obtained. The refining mechanism mainly owed to the increasing constitutional supercooling at the solidification front. Furthermore, the compound Al 2 Nd generated by the reaction of Al and Nd, which distributed at the phase boundary and inside β phase, could also restrain the growth of α phase. Nd could improve the tensile strength and elongation of Mg-8Li-3Al alloy, however, excessive Al 2 Nd might also become crack source and decrease the elongation.

Effects of ultrasonic vibration on solidification structure and properties of Mg-8Li-3Al alloy

Abstract Ultrasonic vibration was introduced into the Mg-8Li-3Al alloy melt during its solidification process. The microstructure, corrosion resistance and mechanical properties of the Mg-8Li-3Al alloy under ultrasonic vibration were investigated. The experiment results show that the morphology of a phase is modified from coarse rosette-like structure to fine globular one with the application of ultrasonic vibration. The fine globular structure is obtained especially when the power is 170 W, and the refining effect also gets better with prolonging the ultrasonic treatment time. The corrosion resistance of the alloy with 170 W of ultrasonic vibration for 90 s is improved apparently compared with the alloy without ultrasonic vibration. The mechanical properties of alloys with ultrasonic vibration are also both improved apparently. The tensile strength and elongation of alloy improve by 9.5% and 45.7%, respectively, with 170 W of ultrasonic treatment for 90 s.

Effects of precipitates on grain size and mechanical properties of AZ31-x%Nd magnesium alloy

The effects of precipitates on grain size and mechanical properties of as-cast AZ31-x%Nd magnesium alloy were investigated, and the affecting mechanism was also discussed. The results indicated that Al2Nd phase, Al11Nd3 phase and a few Al-Mn-Nd-Fe phase were formed when adding 0.38 wt.%–1.46 wt.% Nd into AZ31 melt, coarse Al2Nd transformed into Al11Nd3 gradually with the increasing of Nd content. Due to structure and size transformation and content increasing of Al-Nd phase, the grain size of AZ31-x%Nd alloy increased firstly, and then decreased with the increment of Nd content. After reaching a minimum value, once again it rose up, provided that Nd content was further increased. The tensile property reached its optimal value when the adding amount of Nd content was 1.05 wt.%, however, adding excessive amount of Nd deteriorated both ultimate strength and elongation of AZ31 alloy.

Preparation of closed-cell Mg foams using SiO2-coated CaCO3 as blowing agent in atmosphere

Abstract In melt foaming method, the thermal stability and foaming speed of blowing agent significantly affect the pore structure, pore size and porosity of metal foams. To retard the foaming speed and increase thermal stability, Na2O·nSiO2 and dilute hydrochloric acid were used to coat SiO2 passive layer on the surface of CaCO3 which is the blowing agent of Mg foams. Thermal stability and microstructure of the SiO2 passive layer were studied by thermo gravimetric analyzer-differential thermal analysis (TGA-DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the thermal stability of coated CaCO3 is improved. The SiO2 layer is amorphous with reticular structure. Contrasting experiments reveal that the coated CaCO3 can foam placidly. Moreover, large size and homogeneous Mg foams were prepared without protective gas with the ignition- proof by alloying. And the porosity of the Mg foams is 60%-70%.

Microstructure of Al-Zn-Mg-Cu-Zr-0.5Er alloy under as-cast and homogenization conditions

Abstract The billets of Al-Zn-Mg-Cu-Zr and Al-Zn-Mg-Cu-Zr-0.5Er alloys were prepared by semi-continuous direct chill casting (DCC). The effects of trace Er on microstructure of Al-Zn-Mg-Cu-Zr alloy under as-cast and homogenization conditions were studied. The results show that the grain morphology is large dendritic structure and the grain size increases obviously by the addition of 0.5% Er. Moreover, most of Er element in the alloy segregates at grain boundary during solidification, resulting in ternary Al8Cu4Er phase. After homogenization, most of the MgZn2 phase at grain boundary has dissolved back to Al matrix in the two alloys. In the Er-containing alloy, the dissolution temperature of Al8Cu4Er phase is about 575 °C. Therefore, the homogenization treatment cannot eliminate Al8Cu4Er phase validity.

Microstructure and mechanical properties of Mg-5Gd-2Y-2Zn-0?5Zr alloy

Abstract Microstructures and mechanical properties of the Mg–5Gd–2Y–2Zn–0·5Zr alloy (wt-%) in the as cast and solution treated conditions have been investigated using optical microscopy, scanning electron microscope, X-ray diffraction, electron probe X-ray microanalyser and transmission electron microscope. The results show that after adding the element Y, the as cast Mg–5Gd–2Y–2Zn–0·5Zr alloy forms the Mg12Zn(Y, Gd) phase with 18R-long period stacking ordered (LPSO) structure, and the Gd atoms in the phase can slow down the transition process of 18R to 14H in high temperature treatment. LPSO phase in the grain boundary can ensure the strength of the alloy at room and elevated temperature through effectively preventing grain boundary sliding. At 250°C, the alloy has shown the similar ultimate tensile strength and tensile yield strength under room temperature, 241 and 130 MPa respectively, and both with excellent elongation.

Grain refinement mechanism of Al−5C master alloy in AZ31 magnesium alloy

Abstract Al-5%C master alloy was prepared by powder in situ synthesis process, and its effects on grain refinement of AZ31 alloy and refining mechanism were investigated. The results indicate that the Al-5C master alloy consists of α(Al) and Al4C3 phases, and the size distribution of Al4C3 particles is controlled by sintering time. The Al-5C master alloy can remarkably reduce the grain size of AZ31 alloy, which decreases with the increasing addition amount of Al-5C master alloy when the addition amount is below 2%. The refining mechanism is attributed to the formation of new compounds of Al-C-Mn particles by Al4C3 and Mn, which might act as nucleating substrates for α-Mg grain.

Effects of yttrium on microstructure and mechanical properties of Mg-Zn-Cu-Zr alloys

Abstract The effects of yttrium addition on microstructure and mechanical properties of as-cast Mg-6Zn-3Cu-0.6Zr- x Y ( x =0, 0.5, 1.0, 1.5 and 2.0, mass fraction, %) (ZCK630+ x Y for short in this study) alloys were investigated by means of OM, XRD and SEM. The results show that the average grain size of Mg-Zn-Cu-Zr magnesium alloy is effectively reduced (from 57 μm to 39 μm) by Y addition. The analysis of XRD indicates the existence of I-phase (Mg 3 Zn 6 Y) and W-phase (Mg 3 Zn 3 Y 2 ) in ZCK630 alloys with Y addition. The ultimate tensile strength of ZCK630 alloys is significantly deteriorated with increasing Y addition, which is possibly related to the continuous networks of intergranular phases and the increase of W-phase.

Effect of neodymium, gadolinium addition on microstructure and mechanical properties of AZ80 magnesium alloy

Abstract The microstructure and mechanical properties of AZ80 magnesium alloys with varying Nd, Gd contents were investigated. The results revealed that the as-cast microstructure of AZ80 alloy was composed of α-Mg matrix and divorced eutectic β-Mg 17 Al 12 phases. The fraction of Mg 17 Al 12 phase was reduced when 0.6 wt.% Nd was added, and new rod-shaped Al 11 Nd 3 phase and small block-shaped Al-Nd-Mn phase appeared. With Gd addition, the Gd elements mixed with Nd to form rare earth phases. New block-shaped Al 2 Gd and Al 2 Nd phases which were collectively called Al 2 RE phases were observed in the microstructure with more than 0.6 wt.% Gd addition. Moreover, the addition of Gd could promote the precipitation of block-shaped Al 2 RE phase, and inhibit the original rod-shaped Al 11 Nd 3 phase. The AZ80-0.6Nd-0.6Gd alloy exhibited the optimal mechanical properties among all the experimental alloys, in which the tensile strength, yield strength and elongation were 215, 145 MPa and 8.33%, respectively.

Effects of electromagnetic stirring on microstructure and mechanical properties of super light Mg-Li-Al-Zn alloy

Abstract Effects of electromagnetic stirring on the microstructure and mechanical properties of the magnesium-lithium-aluminum alloy were studied. The results reveal that, the morphology of the α phase changes from the long block to globular structure and β phase distributes more widely in the periphery of α phase when the electromagnetic stirring voltage is higher than 110 V. The mechanical properties are increased significantly with the increasing electromagnetic stirring. The tensile strength is improved from 172 to 195 MPa, and the elongation is increased from 10.65% to 25.75%.