Effect of Zn Concentration on the Microstructure and Mechanical Properties of Al-Mg-Si-Zn Alloys Processed by Gravity Die Casting

Abstract

The microstructure and mechanical properties of Al-8.1Mg-2.6Si-(0.08 to 4.62)Zn alloys (in wt pct) have been investigated by the permanent mold casting process. X-ray diffraction analysis shows that the s-Mg 32 (Al, Zn) 49 phase forms when the Zn content is 1.01 wt pct. With higher Zn contents of 2.37 and 3.59 wt pct, the g-MgZn 2 and s-Mg 32 (Al, Zn) 49 phases precipitate in the microstructure, and the g-MgZn 2 phase forms when the Zn content is 4.62 wt pct. Metallurgical analysis shows that the g-MgZn 2 and s-Mg 32 (Al, Zn) 49 phases strengthen the Al-8.1Mg-2.6Si-(0.08 to 4.62)Zn alloys. After solutionizing at 510°C for 180 minutes and aging at 180°C for 90 minutes, the g¢-MgZn 2 phase precipitates in the a-Al matrix, which significantly enhances the mechanical properties. Addition of 3.59 wt pct Zn to the Al-8.1Mg-2.6Si alloy with heat treatment increases the yield strength from 96 to 280 MPa, increases the ultimate tensile strength from 267 to 310 MPa, and decreases the elongation from 9.97 to 1.74 pct.

Effect of Zn content on microstructure and properties of hypoeutectic and near-eutectic Al-Si alloys

“…Thus, the motion of dislocation becomes easier and the hardness of the system decreases. Another possible reason is that the low zinc content alloys solidify at higher temperatures making it difficult to increase hardness by grain refinement [14][15].…”

The development of low-temperature heat-treatable high-pressure die-cast Al–Mg–Fe–Mn alloys with Zn

“…T' and T'' phases) are often observed in Al-Mg-Zn alloys [5, 7, 8, 19, 20, 25, 26] [22, 23]. However, it was also reported that the precipitate in several cast Al-Mg-Zn alloys with non-negligible Cu or Si levels, including Al-10.2Mg-3.2Zn-2.7Si aged at 160°C [30], Al-8.1Mg-3.5Zn-2.6Si aged at 180°C [10] and Al-5Mg-3.09Zn-1.0Cu aged at 150°C [21], is g' phase. It indicates that the phase transformation between g' and T' or T'' phases in Al-Mg-Zn alloys maybe exists.…”

“…The two most popular improved Al-Mg alloys are Al-Mg-Zn [4][5][6] and Al-Mg-Cu-Zn [7,8], in which T-Mg 32 (Al, Zn) 49 and S-Al 2 MgCu phases and their precursors were formed and largely improve the mechanical properties. Meanwhile, Si is also added into Al-Mg alloys to form the strengthening Mg 2 Si phase and its precursors in Al-Mg-Si-Zn [9][10][11] and Al-Mg-Si-Cu-Zn [12][13][14].…”

Effect of Ti on microstructure and mechanical properties of die-cast Al-Mg-Zn-Si alloy

“…Shouxun Ji [5][6][7] et al developed the Al-Mg 2 Si-Mg-Zn base alloy, they also studied the effect of solid solution and aging treatment on the microstructure and properties of high strength die-cast Al-Mg-Zn-Si alloy, and the mechanical properties were significantly improved compared with the as-cast state. The die-casting alloy is a new type of heat-resistant and reinforced die-casting alloy, which can reduce the solution temperature by 60°C-100°C compared with conventional die-cast alloys.…”