The Effect of Ni on the High-Temperature Strength of Al-Si Cast Alloys

Abstract

In order to investigate the effect of Ni on the high-temperature strength of Al-Si cast alloys, tensile properties of hypoeutectic and eutectic alloys were determined at 250 °C after long-term annealing at test temperature. LOM- and SEM-analysis revealed the existence of Al3Ni-phases in close contact to eutectic Si. It was shown that the strength can be increased by the addition of Ni, though just to a certain level, depending on the fraction of eutectic phase in the alloy. The alloys were considered as a coarse two-phase system where a hardening effect is caused by load transfer to the harder phase, which requires a certain connectivity/contiguity of the latter. The paper describes the extent of contiguity of the eutectic as well as the hard silicon and Al3Ni-phases within the eutectic, and discusses their contribution to an enhanced strength of Al-Si alloys at elevated temperatures.

Effect of main alloying elements on strength of Al–Si foundry alloys at elevated temperatures

“…The compositions of the samples are shown in Table 1. The near eutectic alloys (1)(2)(3)(4)(5)(6)(7)(8) can be divided into an Mg containing (1)(2)(3)(4) and an Mg free group (5)(6)(7)(8), whereas the hypoeutectic alloys are sectioned according to the particular combination of the respective main alloying elements: 9-24 (Cu/Ni) and 25-36 (Cu/Mg). Additionally, all alloys contain Fe and Mn in an amount comparable to recycling Al-Si foundry alloys.…”

“…Therefore, in the last couple of years, several investigations were carried out with the objective of improving the mechanical properties of hypoeutectic and near eutectic Al-Si foundry alloys at elevated temperatures. [1][2][3][4][5][6] Specific alloying elements like Ni, Cu and Mg were observed to improve the high temperature strength of Al-Si foundry alloys to certain limits by various strengthening mechanisms. [1][2][3][4][5][6] However, the positive effect of the four classical strengthening mechanisms, e.g.…”

Effect of Cr content and heat-treatment on the high temperature strength of eutectic Al–Si alloys

“…Li et al [9] reported the HT tensile strength (350 o C) can be elevated from 42.74 MPa to 61.63 MPa with the introduction of Ni to form Al 3 CuNi and Al 7 Cu 4 Ni in Al-13 wt% Si alloy. Similarly, Stadler et al [10,12] added 2.11 wt% Ni into Al-12 wt% Si alloy, which can improve the HT strength (250 o C) from 90 (0 wt% Ni) to 120 MPa (2.11 wt% Ni).…”

The effect of main alloying elements on the physical properties of Al–Si foundry alloys

“…The accelerated need for weight reduction, however, leads to higher mechanical and thermal loading of these aluminium castings in future vehicles, requiring improved Al-Si foundry alloys. Therefore, in the last couple of years, several investigations were carried out with the objective of improving the mechanical properties of Al-Si foundry alloys at elevated temperatures [1][2][3][4][5][6].…”