Morphology and Properties of Mg2Si Phase Modified by Pb in As-Cast Mg-2.5Si-xPb Alloys

Pb plays an important role in determining the morphologies and mechanical properties of the Mg2Si phase in Mg-2.5Si-xPb alloys. As the amount of Pb increases from 0.4 wt.% to 1 wt.%, the primary Mg2Si phase is refined during solidification. Its morphologies transform from equiaxed-dendrite to polygonal and finally to roughly circular. The key reason for morphology evolution is the preferential adsorption of Pb atoms on Mg2Si {100} surfaces to suppress the growth rate along the ⟨100⟩ directions, which is demonstrated by the adsorption model based on first principles. In addition, the hardness of the Mg2Si phase decreases with the increasing solution content of Pb according to the results of the nanoindentation. With the addition of Pb at 1 wt.%, Pb content in the primary Mg2Si phase reaches a maximum of 0.4 wt.%, and the hardness of the primary Mg2Si phase reaches a minimum of 3.64 GPa. This reduction in hardness is attributed to the augmented ionic bond ratio resulting from the solution of Pb, which concurrently enhances the toughness of the Mg2Si phase.

Morphology evolution of primary Mg2Si in Ca-modified Al–Mg2Si alloy with various contents of Mg/Si

The combined influence of Mg/Si and Ca contents on the crystallization of primary Mg2Si in Al–Mg2Si alloy is investigated.

Structure and mechanical behavior of in situ developed Mg2Si phase in magnesium and aluminum alloys - a review

The demand for lightweight, high specific strength alloys has drastically increased in the last two decades. Magnesium and aluminum alloys are very suitable candidate materials. Research on alloys with an Mg₂Si phase started about three decades ago. The current scenario is that magnesium and aluminum alloys containing an Mg₂Si phase are very popular in the scientific community and extensively used in the automotive and aerospace industries. Mg₂Si is a very stable phase and exhibits excellent mechanical, thermal, electrochemical and tribological properties. This paper presents a brief review of Mg–Si binary alloys, and Mg–Si–Al and Al–Si–Mg alloys. Grain refinement methods and mechanical properties have been reported on lightweight alloys containing Mg and Si. The available results show that silicon reacts with magnesium and forms an intermetallic compound with the stoichiometric formula Mg₂Si. There is in situ formation of an Mg₂Si phase in Mg–Si, Mg–Si–Al and Al–Mg–Si alloys by the diffusion or precipitation process. The morphology and size of an in situ developed Mg₂Si phase depend on the synthesis route and base metal or matrix. In the liquid metallurgy process the precipitation sequence depends on the cooling rate. The morphology of the Mg₂Si phase depends on the precipitation sequence and the mechanical properties depend on the morphology and size of the Mg₂Si phase within the alloy matrix.

The demand for lightweight, high specific strength alloys has drastically increased in the last two decades.

Influence of Li₂Sb Additions on Microstructure and Mechanical Properties of Al-20Mg₂Si Alloy

It is found that Li₂Sb compound can act as the nucleus of primary Mg₂Si during solidification, by which the particle size of primary Mg₂Si decreased from ~300 to ~15–25 μm. Owing to the synergistic effect of the Li₂Sb nucleus and adsorption-poisoning of Li atoms, the effect of complex modification of Li-Sb on primary Mg₂Si was better than that of single modification of Li or Sb. When Li-Sb content increased from 0 to 0.2 and further to 0.5 wt.%, coarse dendrite changed to defective truncated octahedron and finally to perfect truncated octahedral shape. With the addition of Li and Sb, ultimate compression strength (UCS) of Al-20Mg₂Si alloys increased from ~283 to ~341 MPa and the yield strength (YS) at 0.2% offset increased from ~112 to ~179 MPa while almost no change was seen in the uniform elongation. Our study offers a simple method to control the morphology and size of primary Mg₂Si, which will inspire developing new Al-Mg-Si alloys with improved mechanical properties.

Effects of Complex Modification by Sr-Sb on the Microstructures and Mechanical Properties of Al-18 wt % Mg₂Si-4.5Cu Alloys

This research was carried out to investigate the influence of Sr–Sb on the microstructures and mechanical properties of Al–18 wt % Mg₂Si–4.5Cu alloys. After the addition of 0.2 wt % Sr–Sb, the morphologies of primary Mg₂Si transformed from equiaxed dendrite to cube in as-cast alloys and the average size of primary Mg₂Si decreased from ~50 to ~20 μm. The shape of eutectic Mg₂Si changed from Chinese script to short rod. After extrusion and T6 heat treatment, the ultimate tensile strength of modified alloy at room temperature (RT) and 100 °C increased respectively from 229 to 288 MPa, and from 231 to 272 MPa. The elongation-to-failure only slightly improved from 2.9% to 3.8% and from 3.3% to 3.7% at RT and 100 °C, respectively. The tensile fracture surface revealed a transition from brittle fracture to ductile fracture after modifying by 0.2 wt % Sr–Sb.