Change of Tensile Properties with Aging Time and Temperature in Al-Si-Cu-Mg 354 Cast Alloys with/without Minor Addition of Ni and/or Zr

J Hernandez-Sandoval,E A Elsharkawi,F H Samuel,A M Samuel,M H Abdelaziz,Jörg M K Wiezorek

doi:10.1155/2021/5551633

Abstract

The principal aim of the present research work was to investigate the effects of minor additions of nickel and zirconium on the strength of cast aluminum alloy 354 at room temperature (25°C). A decrease in tensile properties of ∼10% with the addition of 0.4 wt.% nickel is attributed to a nickel-copper reaction which interferes with the formation of Al2Cu precipitates. The platelet-like phases (Al,Si)3(Zr,Ni,Fe) and (Al,Si)3(Zr,Ti) are the main features observed in the microstructures of the tensile samples of alloys with Zr additions. The reduction in mechanical properties is due to the increase in the percentage of intermetallic phases formed during solidification; such particles would act as stress concentrators, decreasing the alloy ductility. The main effect of Zr addition lies in a significant reduction in the alloy grain size ∼40%, rather than an increase in the mechanical properties. Quality index charts could be used in assessing the effects of the Ni and Zr additions to the base alloy, as well as evaluating the heat treatment relationships to the alloy tensile properties, in particular when the system shows multiple precipitation reactions. Due to the high liquidus temperature of the Al-Zr binary phase diagram, addition of Zr beyond 0.2% is not recommended to avoid undissolved Zr.

Highlights

A decrease in tensile properties of ∼10% with the addition of 0.4 wt.% nickel is attributed to a nickel-copper reaction which interferes with the formation of Al2Cu precipitates. e plateletlike phases (Al,Si)3(Zr,Ni,Fe) and (Al,Si)3(Zr,Ti) are the main features observed in the microstructures of the tensile samples of alloys with Zr additions. e reduction in mechanical properties is due to the increase in the percentage of intermetallic phases formed during solidification; such particles would act as stress concentrators, decreasing the alloy ductility. e main effect of Zr addition lies in a significant reduction in the alloy grain size ∼40%, rather than an increase in the mechanical properties
Starting with the decomposition of the supersaturated solid solution (SSS), followed firstly by the formation of GPB (Guinier–Preston–Bagaryatsky) zones and by the precipitation of the coherent S′′ and the semicoherent S′ and the incoherent equilibrium S (Al2CuMg) phase. e coherent S′′ and the semicoherent S′ precipitates are the main source of hardening in aluminum alloys containing Cu and Mg, and they are responsible for increasing the strengthening level of this type of alloy, whereas over aging conditions result in the precipitation of the incoherent equilibrium S phase
There is another phase containing Si which may form in the Al-Cu-Mg-Si system, called the Q phase or quaternary Al4Mg8Cu2Si6 phase which can form upon solidification or during aging [11,12,13,14]. is Q phase can coexist with Al2Cu, Mg2Si, and Si depending on the ratio between Cu, Mg, and Si

Summary

Introduction

With regard to an aluminum alloy containing Cu and Mg as the hardening elements, the aging treatment results in the formation of a range of precipitates.

Results

Conclusion