Understanding the effect of Ni content on microstructures and tensile properties of AlSi10Mg alloy samples under a variety of solidification rates

Abstract

It is critical to gain a better knowledge of the impact of varying Ni contents on the microstructural changes of the AlSi10Mg alloy solidified at various cooling severities. Understanding the combined features of Si and Al3Ni phases constituting this modified alloy may also have a significant impact on understading its properties. In order to advance in these topics, AlSi10Mg alloys modified with, 1.0, 2.0 and 3.0 wt% Ni are either directionally solidified (DS) at lower cooling rates or laser surface remelted (LSR) at higher rates. α-Al dendritic branches are found in the microstructure of all tested alloys either for DS or LSR specimens, surrounded by the eutectic constituent. Moreover, the dendritic array is defined by the secondary dendritic spacing, λ2, which is found to be 65% lower for the Ni-containing alloys than in the AlSi10Mg alloy. The microstructure of the quaternary alloys is constituted by the α-Al+Si+Al3Ni phases, with the Al3Ni phase having a prevalent fishbone shape and being found in higher proportions as a result of slow cooling and increasing Ni content. Ultimate tensile strength of the AlSi10Mg alloy is 190 MPa for a specified range of λ2 (22–30 µm), which is higher than that of Ni-containing alloys for the same range. However, Ni-containing alloys are more sensitive to λ2, and the DS AlSi10Mg-1Ni alloy, as well as a combination of samples solidified at no less than 3 °C/s, fine dendritic spacing (<18 µm) and fine fishbone+plate-like Al3Ni mixture, shows the best tensile results: 4.6% and 208 MPa. This appears to be the optimal condition for cooperative reinforcement throughout these hardening phases. The laser treated AlSi10Mg-2Ni alloy samples have a superior hardness of 145 HV, much higher than the original substrate, demonstrating the effectiveness of the laser treatment in improving the surface mechanical properties of a Ni-modified AlSi10Mg alloy.