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

Lucia Lattanzi,Maria Di Giovanni,Gian Garagnani,Maverick Giovagnoli,Mattia Merlin,Annalisa Fortini,Emanuela Cerri,Marisa Di Sabatino,Daniele Casari

doi:10.3390/met8040224

Abstract

In recent years, the influence of Ni on high-temperature mechanical properties of casting Al alloys has been extensively examined in the literature. In the present study, room temperature mechanical properties of an A356 alloy with Ni additions from 0.5 to 2 wt % were investigated. The role of Ni-based compounds and eutectic Si particles in reinforcing the Al matrix was studied with image analysis and was then related to tensile properties and microhardness. In the as-cast condition, the formation of the 3D network is not sufficient to determine an increase of mechanical properties of the alloys since fracture propagates by cleavage through eutectic Si particles and Ni aluminides or by the debonding of brittle phases from the aluminum matrix. After T6 heat treatment the increasing amount of Ni aluminides, due to further addition of Ni to the alloy, together with their brittle behavior, leads to a decrease of yield strength, ultimate tensile strength, and Vickers microhardness. Despite the fact that Ni addition up to 2 wt % hinders spheroidization of eutectic Si particles during T6 heat treatment, it also promotes the formation of a higher number of brittle Ni-based compounds that easily promote fracture propagation.

Highlights

Al-Si casting alloys are extensively used in automotive components in order to reduce both weight and fuel consumption
Ni seems to neutralize the positive effects of the T6 heat treatment to some extent
The effect of Ni additions up to 2 wt % on the room temperature tensile properties and Vickers microhardness of the A356 aluminum casting alloy has been investigated in this research paper

Summary

Introduction

Al-Si casting alloys are extensively used in automotive components in order to reduce both weight and fuel consumption. In this respect, in recent years a considerable amount of studies have concerned the improvement of their characteristics by melt inoculation [1], by the addition of alloying elements [2], and by the optimization of heat treatments and process parameters [3,4]. From Cu, Ni has an extremely limited solubility in Al (0.05 wt % at 640 ◦ C, i.e., the eutectic temperature, decreasing down to 0.003 wt % at 527 ◦ C) and, it is mainly found in intermetallic compounds with Al, Cu, or Fe. It has been proved that the presence of Ni in eutectic and hypoeutectic Al-Si alloys leads to the formation of thermally stable ε-Al3 Ni and T-Al9 FeNi intermetallic compounds [9,10,11]. The latter one precipitates through a peritectic reaction from the Metals 2018, 8, 224; doi:10.3390/met8040224 www.mdpi.com/journal/metals

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