Amirthalingam Srinivasan

Development of Magnesium Based Alloys for High Temperature Applications

Individual and combined additions of elements like Si, Sb, Sr are carried out to AZ91 alloy and its microstructure, mechanical properties especially creep properties and corrosion behavior are investigated. In general, additions of the above elements improve the mechanical properties. Further, the results show these alloying elements introduce thermally stable intermetallics and thereby improve the creep performance. Among various additions, Sb addition provides highest creep resistance. With the Si and Sr additions, the corrosion resistance of AZ91 alloy is improved. Detailed micro-mechanisms are also studied and they are correlated with the properties studied.

Influences of Y Additions on the Hot Tearing Susceptibility of Mg-1.5wt.%Zn Alloys

The influences of Y (0.2, 2 and 4 wt.%) additions on the hot tearing behaviour of Mg‑1.5Zn alloys were investigated using a constrained rod casting (CRC) apparatus equipped with a load cell and data acquisition system. The initiation of hot tearing was monitored during CRC experiments. It corresponds to a drop in load on the hot tearing curves. The experimental results indicate that, the hot tearing susceptibility defined by the total crack volume, which was measured by the wax penetration method, decreases with increasing the content of Y at a mould temperature of 250 °C. The reduced susceptibility is attributed to the effect of Y on the solidification behaviour: it shortens the freezing range and reduces the grain size. The highest susceptibility is observed for Mg-1.5Zn-0.2Y alloy. It is caused by its coarse microstructure and relatively larger solidification range. In contrast, the lowest susceptibility is observed for Mg-1.5Zn-4Y alloy with a small equiaxed grain microstructure. In addition, the healing of hot cracks by the subsequent refilling of the remained liquid at the later stage of solidification is also beneficial for the alleviation of hot tearing susceptibility in Mg-1.5Zn-4Y alloy.

Effect of Sb, Sn and Pb Additions on the Microstructure and Mechanical Properties of AZ91 Alloy

This article presents the effect of individual addition of Sb, Sn and Pb on the precipitation sequence at room as well as high temperature tensile properties of AZ91 alloy. The results show grain refinement, formation of Mg3Sb2 and Mg2Sn phases when Sb and Sn are added to AZ91 alloy. Lamellar precipitate is significantly suppressed while Pb added. Improved room and high temperature tensile properties are observed in Sb and Sn addition. Maximum tensile properties are noticed with AZ91 alloy having 0.5 wt.% Sb addition.

LOW-PRESSURE CASTING OF LM25 (Al-7Si-0.3 Mg) ALUMINIUM ALLOY

ABSTRACT Low-pressure casting (LPC) is a specialized process for producing thin component castings of ferrous and nonferrous metals and alloys. This process has fewer casting and mold-filling problems than conventional processes like gravity and pressure-die casting, thus giving rise to castings with good mechanical properties. In the present study, LM25 (Al-7Si-0.3 Mg) aluminium alloy castings have been produced using indigenously designed and developed LPC setup. Using this process, defect-free, quality castings as well as thin castings of thickness down to 2 mm have been successfully cast. The strength properties of LP cast LM25 alloy are found to be higher than those of the gravity cast alloy. The microstructure of LPC aluminium alloy is seen with fewer casting defects and less porosity.

Microstructure, Mechanical and Corrosion Properties of Mg-Gd-Zn Alloys

Microstructure, mechanical and corrosion properties of Mg-10Gd-2Zn and Mg-10Gd-6Zn (all in wt.%) were evaluated in the as-cast condition. The microstructures of both alloys contained (Mg, Zn)3Gd phase at the interdendritic regions and long period stacking ordered (LPSO) phase distributed in the matrix. The Mg-10Gd-6Zn alloy consisted of a high volume fraction of (Mg,Zn)3Gd intermetallic phases continuously distributed along the grain boundaries. The tensile properties, especially the elongation to failure of the Mg-10Gd-6Zn alloy were slightly lower than those of Mg-10Gd-2Zn. An enhancement in creep resistance was observed with Mg-10Gd-2Zn alloy with the post creep tested microstructure showing dynamic precipitation. Corrosion studies indicated that increased Zn content, from 2 to 6 % in Mg-10Gd alloys, significantly reduced the corrosion resistance.

Grain Refinement Mechanism in Al–4B Master Alloy Added Pure Mg

Al–4B master alloy has been prepared by the reaction of fluoride salt KBF4 with molten Al and different amounts of this master alloy (0.5, 1, 1.5 and 2 wt%) has been added to pure Mg to study in detail its effect on the grain refinement of pure Mg. Considerable reduction in grain size from 1300 to 210μm is obtained and maximum reduction is observed with 2 wt% master alloy addition. The grain refinement is caused by both the growth restriction effect of Al and the presence of potent AlB2 nucleant particles. Improvement in mechanical properties is obtained with Al–4B master alloy and is attributed to increase in grain boundary area due to the grain refinement and the particle strengthening due to AlB2.

Effects of gadolinium addition on the microstructure and mechanical properties of Mg–9Al alloy

This research aims to study the significance of Gd addition (0wt%–2wt%) on the microstructure and mechanical properties of Mg–9Al alloy. The effect of Gd addition on the microstructure was investigated via X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The Mg–9Al alloy contained two phases, α-Mg and β-Mg17Al12. Alloying with Gd led to the emergence of a new rectangular-shaped phase, Al2Gd. The grain size also decreased marginally upon Gd addition. The ultimate tensile strength and microhardness of Mg–9Al alloy increased by 23% and 19%, respectively, upon 1.5wt% Gd addition. We observed that, although Mg–9Al–2.0Gd alloy exhibited the smallest grain size (181 μm) and the highest dislocation density (5.1 × 1010 m−2) among the investigated compositions, the Mg–9Al–1.5Gd alloy displayed the best mechanical properties. This anomalous behavior was observed because the Al2Gd phase was uniformly distributed and present in abundance in Mg–9Al–1.5Gd alloy, whereas it was coarsened and asymmetrically conglomerated in Mg–9Al–2.0Gd.

A Comparative Study on Corrosion Behavior of Mg-Zn-Gd Alloys by Varying the Gd Content

In this study, two Mg-Zn-Gd alloys (Mg-5Zn-5Gd and Mg-5Zn-3Gd) are fabricated using high purity raw materials and by a clean melting process and subjected to immersion testing. The results indicate an increase in corrosion rate for increase in Gd content and the results are correlated using SEM, XRD and EDS analyses. It is seen that RE addition provides a protective oxide coating over the sample surface thereby assisting the corrosion resistance.

Effect of Si on the Microstructure and Mechanical Properties of Mg-2Sb Alloy

In the present work the effects of Si (0.5, 1, 1.5 wt%) on the as cast microstructure of Mg-2Sb alloy have been investigated. Si addition forms new Mg-Sb-Si ternary compound in Mg-Sb alloys besides the morphology of Mg3Sb2 changes from needle to chinese scripted and polygonal shaped Mg-Sb-Si ternary compound. The improved room temperature tensile properties are obtained with Mg-2Sb-1Si alloy which is due to the presence of polygonal shaped Mg-Sb-Si ternary compound.