Chun-li Guo

Protective compound coating on AZ91D Mg alloy fabricated by combination of cold spraying with die casting

A novel processing that leads to the formation of a protective compound coating upon the AZ91D Mg alloy by the combination of cold spraying of Al–Mg alloy on a die cavity surface with subsequent die casting was discussed. The microstructure and phase composition of the coating were investigated using X-ray diffraction and scanning electron microscope coupled with energy dispersive spectroscopy. Results revealed that the coating consisted mainly of β phase (Mg17Al12) plus some Al and integrated with the substrate by mechanical interlocking and slender metallurgical bonding formed during the die casting process. A high bond strength of 82±5 MPa for the coating was achieved. The hardness and wear resistance of the AZ91D Mg alloy were greatly improved due to the compound coating. Simultaneously, the results of immersion tests and electrochemical corrosion tests indicated that the coated AZ91D Mg alloy specimens had better corrosion resistance compared with the bare AZ91D alloy specimen.

Corrosion fatigue behavior of epoxy-coated Mg–3Al–1Zn alloy in gear oil

Abstract The corrosion fatigue behavior of epoxy-coated Mg–3Al–1Zn alloy in gear oil was investigated. The corrosion and the fracture surfaces after fatigue test were analyzed by scanning electron microscopy (SEM) and the corrosion compositions were measured by energy-dispersive spectrometry (EDS). The fatigue properties and the crack initiation mechanisms of the specimens before and after epoxy coating treatment were discussed. The results indicate that the fatigue limit after epoxy coating treatment in gear oil is higher than that of the uncoated specimens. The epoxy coating is an excellent way to prevent direct contact between the Mg–3Al–1Zn alloy and surrounding environments. The mechanical properties of the epoxy coating layer are lower than that of magnesium alloy, which is the main reason for the fatigue crack initiation on the epoxy coating layer. In addition, the gear oil lubrication could lead to the flaking off of the epoxy-coated layer.

High-frequency corrosion fatigue behavior of AZ31 magnesium alloy in different environments

The high-frequency corrosion fatigue behavior of extruded AZ31 magnesium alloy was investigated in different environments: air, gear oil and 3.5% NaCl solution. Compared with that in air, the corrosion fatigue limits were degraded by approximately 3.52% and 58.91%, respectively, and the corrosion fatigue lives were shortened by about 13.43% and 89.36%, respectively. In the same environment, the high-frequency fatigue limits are all higher than those tested at low frequency. The specimen geometrical shape plays a certain factor on stage characteristics of S–N curves. Compared with that of arc transition specimens, the stress sensitivity of line transition specimens is only reflected in a relatively high cycle fatigue life region. Different environments influence the corrosion failure kinetics processes (the crack initiation mechanism), but do not change the fatigue fracture mechanism of the alloy, and the higher loading frequency only accelerate the crack nucleation processes.

Wear and electrochemical behaviour of Mg–Al intermetallic coating

Abstract An erbium modified Mg17Al12 based coating was fabricated by hot press sintering on as extruded AZ61 Mg alloy. The Er modified coating was composed of Mg17Al12 and Al3Er phases. As a result of the presence of the dispersed Al3Er phase, the coating had a greater microhardness than Mg17Al12. Thermal effects of sintering at 400°C for 1 h caused no obvious deterioration in the wear resistance of the AZ61 Mg matrix. Electrochemical and wear resistance tests showed that the Er modified Mg17Al12 based coating had a lower corrosion current density and a lower friction coefficient than Mg17Al12, the AZ61 Mg matrix and a thermal diffusion coating (TDC). The superior wear resistance of the sintered coating resulted from the hard Al3Er phase. The corrosion resistance of the sintered coating was better than that of the TDC as a result of suppression of hydrogen evolution by the rare earth metal Er.

Effect of erbium on microstructures and properties of Mg-Al intermetallic

Abstract The effect of the rare earth element Er on the microstructures and properties of Mg-Al intermetallic were studied in this experiment. Metallographic and X-ray diffraction (XRD) results showed that the microstructures of Mg-Al-Er alloys varied with Er content. The Mg-44Al-0.5Er and Mg-43.8Al-1.0Er alloys were both composed of Mg 17 Al 12 matrix and Al 3 Er phase, whereas Mg-43Al-3.0Er and Mg-42Al-5.0Er were composed of Mg 17 Al 12 matrix, Al 3 Er phase, and Mg-Mg 17 Al 12 eutectic. The Mg-42Al- 5.0Er alloy showed the highest microhardness, and the values remained nearly stable as Er content increased from 1.0 wt.% to 5.0 wt.%. The dispersed second phase Al 3 Er caused the grain refinement of the Mg-Al-Er alloy, which was the main reason for the improvement in microhardness. The corrosion resistance of the Er-containing alloys initially increased and then decreased with increasing Er content. All the Er-containing alloys had the ability to suppress hydrogen evolution, which was the main reason for the higher corrosion resistance of the modified alloys than that of the Mg-44.3Al alloy. Considering the higher hardness and dispersity of the Al 3 Er phase, Mg-43.8Al-1.0Er exhibited higher wear resistance than the as-cast Mg-44.3Al alloy.