Calculation Based on the Formation of Mg2Si and Its Effect on the Microstructure and Properties of Al–Si Alloys

Abstract

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.

The effect of cold rolling on mechanical properties and microstructure of aluminium 6082 T6 joint by friction stir welding process

“…FSW can improve mechanical properties such as fracture toughness, fatigue, and ductility (Hao et al, 2021) .Looking at the fracture mode of four samples of cold reduced material highlighted in figure 4b shows that the material is more ductile as compared to as-received material and this justifies why there is less decrease in mechanical properties on it as compared to as-received FSW welded material. Some of the deviations that might have influence in the results of tensile tests are hooking defects which is one of the most common defects observed in FSW lap joints, which results in a decrease of mechanical properties in the weld when found in the load path (Gungor et al, 2014) to the material used in this study.…”

“…The second phases identified were Mg2Si shown on both cold rolled and as-received material WZ. Mg2Si has a low density (1.90 g/cm3), a high melting point (1087 ºC), a high hardness (4.5×10^9 N/m^2) , a high modulus of elasticity around (120 GPa) and a low thermal expansion coefficient (7.5×10^9) and will have a great influence on the mechanical properties of the material (Hao et al, 2021). Mg2Si phases identified on the welded zone of both samples are surrounded by α-Al (white spots), which contain silicon.…”

The Influence of Foundry Scrap Returns on Chemical Composition and Microstructure Development of AlSi9Cu3 Alloy

“…This was due to the nature of the analysis, which also analysed the background of the sample. The phases were determined on the basis of EDS analyses and previous reports [17,18,[20][21][22][23].…”

The Role of Mg Content and Aging Treatment on the Tensile and Fatigue Properties of Die-Cast 380 Alloy

“…Another observation that can be made from Figure 5a is that the undercooling (TG-TN) associated with the development of the α-Al network is more explicit than those observed for the (Al-Si) and (Al-Al2Cu) eutectic reactions. The importance of the ∆Tα undercooling is that it defines the degree of the alloy grain refining [29,30]. It has been reported that the addition of a high percentage of Fe to die-cast alloys prevents the soldering of the casting with the steel die.…”