Hao Hai

Microstructures and mechanical characteristics of electromagnetic casting and direct-chill casting 2024 aluminum alloys

Electromagnetic casting (EMC) technology depends on the electromagnetic force to prevent the metal from touching the mold, leaving the ingot surface very smooth. As a result, the surface imperfections, such as oscillation and subsurface segregation etc. caused by a mold of direct-chill casting (DCC), are avoided. Moreover, the electromagnetic stirring makes the structure become more homogeneous over the entire cross-section. In this paper, 2024 aluminum alloys made by EMC and DCC were analyzed by optical microscope and scanning electron microscope, solution heat treatment and artificial aging was given to investigate the mechanical properties such as hardness, wear resistance and fatigue. Results showed EMC ingots had fine and uniform grain structure, which made the EMC ingots have high hardness and good fatigue. The hardness of EMC specimens increased one time than DCC ones and the fatigue was three times as high as DCC ones in as-cast state. The EMC specimens also expressed an excellent characterization in wear resistance; the weight loss was only a half of DCC specimens.

Effect of Hot Extrusion on Microstructures and Properties of TiB2Effect of Hot Extrusion on Microstructures and Properties of TiB2/AZ31 Magnesium Based Composites/AZ31 Magnesium Based Composites

Abstract The TiB 2 /AZ31 magnesium based composite was fabricated by the in-situ synthesis-semisolid stirring technique, and its microstructure and mechanical property were studied. The results show that hot extrusion not only significantly refines the microstructure of the alloy, but also effectively improves the uniformity of TiB 2 particles distribution. Compared with as-cast AZ31 magnesium alloy, the hardness and tensile strength of as-cast TiB 2 /AZ31 magnesium based composites increase to some extent (unobvious), but the elongation decreases. However, after extrusion, the hardness and the tensile strength of the as-extruded TiB 2 /AZ31 magnesium based composite increase by 126.2% and 98.8%, reaching 950 MPa and 322 MPa, respectively, and the elongation is also higher. Adding of TiB 2 particles to AZ31 alloy and hot extrusion are effective ways to improve the wear resistance of AZ31 magnesium alloy.