Mechanical Properties of Commercial Purity Aluminum Modified by Zirconium Micro-Additives

Ahmad Mostafa,Wail Adaileh,Adnan Kilani,Alaa Awad

doi:10.3390/cryst11030270

Ahmad Mostafa, Wail Adaileh + Show 2 more

Open Access

https://doi.org/10.3390/cryst11030270

Copy DOI

Journal: Crystals	Publication Date: Mar 9, 2021
Citations: 5	License type: CC BY 4.0

Affiliation: Tafila Technical University, University of Jordan

Abstract

The mechanical properties and the fractured surfaces of commercial purity aluminum modified by zirconium micro-additives were investigated by means of experimental examination. A commercial purity Al specimen was used as a reference material and seven Al-Zr alloys in the 0.02–0.14 wt.% Zr composition range (with 0.02 wt.% Zr step) were prepared by microalloying methods. Optical microscopy was used to examine the microstructures and to calculate the grain sizes of the prepared specimens. The phase assemblage diagrams were plotted and the relative amounts of solid phases were calculated at room temperature using FactSage thermochemical software and databases. Proof stress, strength coefficient and strain hardening exponent were measured from the stress-strain curves obtained from tensile experiments and Charpy impact energy was calculated for all specimens. The experiments showed that the grain size of commercial purity Al was reduced by adding any Zr concentration in the investigated composition range, which could be due to the nucleation of new grains at Al3Zr particle sites. Accordingly, the microhardness number, tensile properties and Charpy impact energy were improved, owing to the large grain-boundary areas resulted from the refining effect of Zr, which can limit the movement of dislocations in the refined samples. The basic fracture mode in all specimens was ductile, because Al has an FCC structure and remains ductile even at low temperatures. The ductile fractures took place in a transgranular manner as could be concluded from the fractured surface features, which include voids, ridges and cavitation.

Highlights

Characterizing the mechanical properties of metals and alloys is fundamental for multiple technological applications
One way to modify the Al grain structure is by introducing small amounts of alloying elements, the so-called grain refiners, such as rare earth elements, transition metals and binary alloys (Ti+B) [5,10]
This work aims at investigating the effects of minor Zr additives in the 0.02–0.14 wt.% Zr range on the microstructure, microhardness, tensile properties, and Charpy impact energy of commercial purity aluminum

Summary

Introduction

Characterizing the mechanical properties of metals and alloys is fundamental for multiple technological applications. The main role of the grain refiners is to develop fine equiaxed Al solid solution (FCC_Al) grains in the cast structure either by increasing the number of nucleation sites or by grain multiplications [11]. The addition of transition metals, such as Zr [12], can modify the cast Al structure effectively by forming the Al3Zr primary phase particles [13,14]. It has been reported that the grain refinement effect on the parent metal is often associated with peritectic systems [14,15]. The peritectic reaction progresses and transforms the primary crystals into secondary phase crystals, which act as nuclei for solidification of the remaining melt [15]. The role of the new nucleation sites is to block the grain boundary or sub-boundary migration, which refine the cast grain structure [19,20]

Objectives

Methods

Results