Effect of nickel on the microstructure and mechanical property of die-cast Al–Mg–Si–Mn alloy

Abstract

The effect of nickel on the microstructure and mechanical properties of a die-cast Al-Mg-Si-Mn alloy has been investigated. The results show that the presence of Ni in the alloy promotes the formation of Ni-rich intermetallics. These occur consistently during solidification in the die-cast Al-Mg-Si-Mn alloy across different levels of Ni content. The Ni-rich intermetallics exhibit dendritic morphology during the primary solidification and lamellar morphology during the eutectic solidification stage. Ni was found to be always associated with iron, forming AlFeMnSiNi intermetallics and no Al 3 Ni intermetallic was observed when Ni concentrations were up to 2.06wt% in the alloy. Although with different morphologies, the Ni-rich intermetallics were identified as the same AlFeMnSiNi phase bearing a typical composition of Al (Fe,Mn) [2][3][4][5][6][7] SiNi [4][5][6][7][8][9]. With increasing Ni content, the spacing of the -Al-Mg 2 Si eutectic phase was enlarged in the Al-Mg-Si-Mn alloy. The addition of Ni to the alloy resulted in a slight increase in the yield strength, but a significant decrease in the elongation. The ultimate tensile strength (UTS) increased slightly from 300 MPa to 320MPa when a small amount (e.g., 0.16wt. %) of Ni was added to the alloy, but further increase of the Ni content resulted in a decrease of the UTS. Keywords: Aluminium alloy; microstructural evolution; mechanical properties; Ni-rich compounds; high pressure die casting; CALPHAD modelling IntroductionIn the manufacture of fuel efficient transport systems, weight reduction through the use of lightweight materials remains a very successful and simple means of improving fuel economy and reducing harmful emissions. Increases in aluminium alloys usage for automotive applications provide significant opportunities for weight reduction and therefore real scope to achieve environmental goals, when compared to a conventional steel-based vehicle [1,2]. A 100kg reduction in car weight leads to a saving of 10g CO 2 per kilometre [3]. Aluminium's weight to strength ratio and its high recyclability potential has resulted in a number of aluminium intensive vehicles being released by major automotive manufacturers. This light-weighting strategy has resulted in a decrease of CO 2 produced during the vehicle use phase and also in the manufacturing stage by reducing the use primary aluminium through utilising end-of-life vehicles (ELVs) metal scrap recycling [4,5]. Up to 75% of aluminium recycled in Europe has been used for applications in transportation [6]. The re-use of recycled metal scraps is an important factor for the closed-loop material cycles to support circular economies in accordance with ecological principles [ 7 , 8 ]. Consequently, it is important and essential to understand more about the recycling of aluminium alloys. In recycling aluminium alloys, the unchecked accumulation of impurities will result in the solute concentrations of these elements exceeding the limitation of the registered specification, this restricts the applicati...

The effects of varying Mg and Si levels on the microstructural inhomogeneity and eutectic Mg2Si morphology in die-cast Al–Mg–Si alloys

“…Up to now, the effects of compositional variation on the solidified microstructure and mechanical properties of Al-Mg-Si alloys have been the subject of many studies. For example, Yan [6] reported that Mg addition transformed eutectic Mg 2 Si to primary Mg 2 Si and significantly improved the mechanical properties of Al-Mg-Si alloys, Yang [7] reported that Ni enlarged the spacing of Al-Mg 2 Si eutectic phase and resulted in a slight increase in the yield strength but a significant decrease in elongation, and Ji [3,8,9] also reported the improving the effect of Ti, Fe and Zn on mechanical properties of Al-Mg-Si alloys. Meanwhile, the microstructural inhomogeneity of an individual HPDC Al-5Mg-1.5Si-0.6 Mn-0.2Ti alloy (all compositions quoted in this paper are in wt % unless otherwise stated) has also been reported [3].…”

The formation mechanism of Al6(Fe, Mn) in die-cast Al–Mg alloys

“…In die-cast aluminium alloys, Fe is a common impurity as it is unavoidably picked up in practice. This is mainly because molten aluminium can dissolve steel tools and processing equipment to increase the Fe content in melt [1,2]. As so far, there are no economically profitable methods to completely remove the Fe contents from melt.…”

Room Temperature Mechanical Properties of A356 Alloy with Ni Additions from 0.5 Wt to 2 Wt %

“…High-temperature compression strength is an important requirement for piston alloys since these components have to withstand severe compression stresses, as well as temperatures up to 400 • C during their service life [5,9]. Additionally, some authors investigated the influence of Ni on room-temperature mechanical properties [19,20]. Yang et al [19] reported that the evolution of Ni-rich compounds has a beneficial effect on the room temperature mechanical properties of an Al-Si piston alloy; moreover, the elevated temperature tensile strength was observed to increase by about 19.7%.…”

“…Yang et al [19] reported that the evolution of Ni-rich compounds has a beneficial effect on the room temperature mechanical properties of an Al-Si piston alloy; moreover, the elevated temperature tensile strength was observed to increase by about 19.7%. Yang et al [20] found that the addition of Ni to an Al-Mg-Si-Mn alloy resulted in a slight increase in both room temperature yield strength and ultimate tensile strength.…”