The microstructure and cracking characteristics of MIG welded magnesium alloy (AZ91D) joint, and the effect of welding speed on cracking susceptibility have been investigated. The welded joint consists of primary a-Mg and divorced phases (eutectic a-Mgϩeutectic b-Mg 17 Al 12 ), the latter mainly distributing along the a-Mg grain boundaries. Solidification cracking often occurred in the crater and was also observed at weld center line when welding speed was 300 mm/min, which are associated with segregation of Mn, Al and Zn and high tensile stresses in the welds. Liquation cracking appeared in HAZ immediately adjacent to the fusion line when low welding speed was used (300 mm/min). It is mainly related to the low welding speed resulting in increasing heat input and tensile stresses in the HAZ. It is favorable to decrease heat input for improving the susceptibility of hot cracking during MIG welding of magnesium alloys.

The microstructure and cracking characteristics of MIG welded magnesium alloy (AZ91D) joint, and the effect of welding speed on cracking susceptibility have been investigated. The result indicates the welded joint consists of primary α-Mg and divorced phases (eutectic α-Mg + eutectic β-Mg17Al12), the latter mainly distributing along the α-Mg grain boundaries. The weld of the magnesium alloy displays a high cracking susceptibility. The cracks are mainly formed in the arc crater at the end of the weld. These cracks propagate along the α-Mg grain boundary, and they belong to the solidification cracking. These solidification cracks are resulted by the joint function of the low melting point liquid film in the weld and the tensile stress suffered by the weld metal during the solidification process. The low melting point liquid film is the internal cause to form the solidification cracks, while the tensile stress is a necessary condition. Limiting the amount of the low melting point eutectic and decreasing the tensile stress of the welding joint are two effective methods to improve the solidification cracking susceptibility of the magnesium alloy weld.

Magnetic iron oxide nanomaterials (e.g. Fe3O4 and γ-Fe2O3) with different morphologies have aroused extensive attention due to their fundamental research and potential technological applications such as magnetic recording media, magnetic fluids and magnetic drug-targeting. In this article Fe3O4 nanosheets were successfully synthesized using triblock copolymer (PEO)20(PPO)70(PEO)20 (P123) micelles as structure-directing agents in the presence of surfactant-assisted ethylene glycol (EG) and precipitator hexamethylenetetramine (HMTA) at 70 °C for 2 h in N2. The Fe3O4 nanosheets have irregular shape with thickness of the Fe3O4 nanosheets about 10-15 nm. The X-ray diffraction (XRD) pattern confirms the Fe3O4 nanosheets have magnetite structure and its nine distinguishable diffraction peaks can be perfectly indexed to the (111), (220), (311), (222), (400), (422), (511), (440), and (533) planes of the fcc structure of magnetite. Its saturation magnetization (σs) is 58.4 emu/g. The possible formation mechanism of the Fe3O4 nanosheets in present work is proposed.