Some Investigations on Friction Stir Processed Zone of AZ91 Alloy
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TECHNICAL PAPER
TP 2620
Some Investigations on Friction Stir Processed Zone of AZ91 Alloy H. S. Arora • H. Singh • B. K. Dhindaw H. S. Grewal
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Received: 29 June 2012 / Accepted: 16 September 2012 / Published online: 9 October 2012 Indian Institute of Metals 2012
Abstract In this study, AZ91 based hybrid nanocomposite was fabricated using mixture of TiC and alumina by friction stir processing (FSP). FSP of AZ91 was conducted with as well as without particle addition and under different cooling conditions. Distribution of nano TiC and Al2O3 particles in the Mg matrix was studied using SEM. Grain size analysis of the as-cast and FSP AZ91/(TiC ? Al2O3) composite was done using optical microscopy. The performance of the fabricated nanocomposite was investigated using microhardness, bulk hardness and scratch tests. Microhardness testing was done at 50 gf load and bulk hardness at 5 Kgf load. Scratch test was performed at 2 and 5 N normal load values on a universal tribometer using Rockwell indentor. AZ91/(TiC ? Al2O3) composite exhibited improved mechanical properties. Keywords Magnesium alloy Friction stir processing Hybrid nanocomposite
1 Introduction Mg alloys, owing to their low density and high stiffness to-weight ratio, are gaining increasing importance as a structural material for applications in which weight reduction is critical. However, Mg alloys have not traditionally been used
H. S. Arora (&) H. Singh H. S. Grewal School of Mechanical, Materials and Energy Engineering, Indian Institute of Technology Ropar, Rupnagar 140001, Punjab, India e-mail: [email protected] B. K. Dhindaw School of Minerals, Metallurgical and Materials Engineering, Indian Institute of Technology Bhubaneswar, Orissa 751001, India
for high performance applications due to their low mechanical properties at room and elevated temperatures [1]. A magnesium based alloy designated as AZ91 is widely used to produce cast components due to its excellent castability and reasonable mechanical properties [2]. The microstructure of as-cast AZ91 alloy is characterized by Al-lean dendrites with a eutectic Al-rich solid solution and intermetallic b-Mg17Al12 [3], as well as some porosity defects. The eutectic b-Mg17Al12 with a network-like morphology is mainly distributed at the grain boundaries [2]. Due to its special cast structure, the ascast AZ91 alloy usually exhibits low mechanical properties, so it is necessary to modify the morphology, size and distribution of the b-Mg17Al12 phase and to refine the grains to improve the mechanical properties [2]. Friction stir processing (FSP) is a relatively novel multifunctional metal working method developed, based on the basic principles of friction stir welding (FSW) [4–7]. During FSP, frictional heating between the workpiece and the FSP tool shoulder results in partial melting of the material and the characteristic nugget zone of the friction stir processed region results from the solidification of the partially melted material. This method has been successfully used to modify the micro
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