High-Temperature Tensile Fractography of Zr-, Ni-, and Mn-Containing Al-Si-Cu-Mg Cast Alloys

M H Abdelaziz,E M Elgallad,H W Doty,A M Samuel,F H Samuel

doi:10.1155/2020/9027534

Abstract

This study investigated the fracture behavior of 0.3% Zr-containing 354 alloy following the addition of 0.75% Mn or 2%Ni. The examined surfaces were obtained from tensile testing of the bars at 250°C. For each alloy, the test bar samples were examined in the T6-treated conditions after being exposed to 250°C for 1 and 200 hours. The fracture surface of the base alloy (0.3% Zr-containing 354 alloy) after stabilization for one hour at 250°C reveals a dimpled structure throughout, indicating the ductile nature of the fracture mode. The Alx (Zr, Ti)Si complex compound is observed with star-like and blocky morphologies, with cracks appearing in various particles of this compound. By increasing the stabilization time up to 200 hours, coarser and deeper dimples are formed, highlighting the increased ductility of the alloy due to the softening behavior associated with the prolonged exposure at 250°C. In the one-hour stabilized T6-treated condition alloy containing 2% Ni tested at 250°C, the appearance of microcracks in the Ni-rich phases and the lower density of dimples on the fracture surface compared to those observed in the base alloy emphasize the low ductility of alloy due to Ni-containing intermetallics. Examination of the fracture surface of Mn-containing alloys revealed the advantageous role of sludge particles in resisting the propagation of cracks that developed in many intermetallic phases.

Highlights

Among the category of Al-Si alloys, there are three major alloy systems in the 3xxx series, i.e., Al-Si-Mg, Al-Si-Cu, and Al-Si-Cu-Mg systems. e 354-type alloy belongs to the AlSi-Cu-Mg system, along with the well-known B319 alloy
Nam and Lee [9], Lee et al [10], and Park and Nam [11] reported that the addition of 0.5 wt% or higher levels of Mn to Al alloys will enhance the strength values significantly without affecting the ductility. e same trend was observed by Garza-Elizondo [12] with the addition of 0.75 wt% Mn to Al-Si-Cu-Mg alloys. e increased amount of Mn in Al-Si-Cu-Mg alloys resulted in the transformation of the β-phase needles into α-phase in script-like form and as large polygonal particles. ese large particles were similar in morphology to the commonly known sludge particles, without Cr. us, Garza-Elizondo [12] concluded that the presence of these
As the addition of transition elements was shown to be beneficial from the point of view of enhancing the precipitation strengthening of trialuminides [23,24,25], Ni and Mn were added to the Zr-containing Al-SiCu-Mg alloy in this study in an attempt to enhance the room- and elevated-temperature mechanical properties of such alloys used in automotive engine components. us, Zr was added to the 354 alloy used in this study to form the base or reference alloy, and other elements (Ni and Mn) were subsequently added individually to study their effect with Zr on the fracture behavior of 354 alloy pulled at elevated temperature (250°C)

Summary

Research Article

High-Temperature Tensile Fractography of Zr-, Ni-, and Mn-Containing Al-Si-Cu-Mg Cast Alloys. Is study investigated the fracture behavior of 0.3% Zr-containing 354 alloy following the addition of 0.75% Mn or 2%Ni. e examined surfaces were obtained from tensile testing of the bars at 250°C. E fracture surface of the base alloy (0.3% Zr-containing 354 alloy) after stabilization for one hour at 250°C reveals a dimpled structure throughout, indicating the ductile nature of the fracture mode. In the one-hour stabilized T6-treated condition alloy containing 2% Ni tested at 250°C, the appearance of microcracks in the Ni-rich phases and the lower density of dimples on the fracture surface compared to those observed in the base alloy emphasize the low ductility of alloy due to Ni-containing intermetallics. Examination of the fracture surface of Mn-containing alloys revealed the advantageous role of sludge particles in resisting the propagation of cracks that developed in many intermetallic phases

Introduction

Alloy description

Results and Discussion

Ti Ti

Fe Cu Cu