In order to investigate the effect of Mg2Si formation on the microstructure and properties of an Al−Si alloy, the critical point of a hypereutectic Al−17Si−4Cu−Mg alloy was calculated by Pandat software. The calculation results of the equilibrium phase diagram show that the critical point for Mg2Si phase formation for the alloy was obtained when the Mg content was 2.2%. The contents of 0.5 wt.% Mg and 2.5 wt.% Mg were selected as the research object. The content of Mg increased from 0.5 wt.% to 2.5 wt.%, the eutectic Si in the matrix was reduced, and the Chinese character-like Mg2Si phase appeared in the microstructure. In the peak ageing state, in addition to θ″ and Q′ phases that were mainly precipitated, there was also needle-like β″ precipitation in the 2.5 wt.% Mg content alloy. Larger precipitates were found in 2.5 wt.% content alloys, mainly due to the promotion of the solid solution having the aggregation and segregation of more solute elements in the matrix. The tensile strength, elongation, and hardness of hypereutectic Al−17Si−4Cu−0.5Mg alloy under peak ageing were 331 MPa, 3.11%, and 152.1 HB, respectively. The tensile strength and the elongation decreased while the hardness increased with the 2.5 wt.% Mg content, which is due to the formation of hard and brittle Mg2Si and Al8FeMg3Si, which has a splitting effect on the matrix.

No abstract

To adjust the morphology of the Si phase and improve the mechanical properties of Al–Si–Cu–Mg alloy formed by semisolid squeeze casting, the effects of solution time on microstructure evolution and mechanical properties are systematically studied. Results show that spheroidization occurs in the Si phase, and the content of Cu in the matrix increases simultaneously after solution treatment at 525 °C for 1 h. As solution time increases to 8 h, the content of Cu in the matrix increases from 1.15% to 1.41% and the dislocation density decreases. After an aging treatment at 180 °C for 12 h, the β′, θ′, and Q′ phases precipitate. After heat treatment, the alloy strength value shows a “double peak” phenomenon. After a 1 h solution treatment, the tensile strength of the alloy reaches the first peak, which is mainly ascribed to the large dislocation density induced by the semisolid squeeze casting process. When the solution time is 8 h, the tensile strength of the alloy is 323 MPa and the tensile strength reaches the second peak, which is ascribed to the rounding of the Si phase and the strengthening effects of fine precipitates.

Effect of electromagnetic stirring and solution treatment on the microstructural evolution and mechanical properties of AZ31 alloy are investigated in this study. Results show that the mechanical properties of AZ31 alloy are substantially increased after electromagnetic stirring and solution treatment. The tensile strength and elongation are 178 MPa and 19.6 % for AZ31 alloy prepared by electromagnetic stirring after solution treatment. A large number of twins and low angle boundaries are observed in the specimen after heat treatment, since the compressive stress on (101‾0 ) crystal plane become larger during quenching. The dislocation arrays, which produced by slip or climbing of dislocations, join together to form low angle boundaries.

The raw materials for extruded preparing magnesium alloy tubes were electromagnetic stirring (EMS) AZ31 magnesium alloy billets and conventional casting (CC) AZ31 magnesium alloy billets. According to the findings, the mechanical properties of the EMS extrusion tubes were far superior to those of the CC extrusion tubes. The key explanation was that the samples of EMS billet had variable initial grain sizes and twin boundaries, which provide additional nucleation sites for DRX nucleation during the extrusion process. With the increase of extrusion temperature and extrusion ratio, the elongation of the tube is further improved. During the extrusion process, the recrystallization mechanism changed from continuous dynamic recrystallization (CDRX) to discontinuous dynamic recrystallization (DDRX).