The AZ61A Mg alloy is heat treated at the temperature of 2600C (5000F) and ... usually heat treated either to improve mechanical properties or as means of ...
International Journal of Metallurgical & Materials Science and Engineering (IJMMSE) ISSN 2278-2516 Vol. 3, Issue 4, Oct 2013, 39-48 © TJPRC Pvt. Ltd.
EFFECT OF HEAT TREATMENT ON TENSILE STRENGTH, HARDNESS AND MICROSTRUCTURE OF AZ61A MAGNESIUM ALLOY S. THIRUMALVALAVAN1, R. SENTHIL2 & A. GNANAVELBABU3 1
Assistant Professor, Department of Mechanical Engineering, Arunai Engineering College, Tamil Nadu, India
2 3
Professor & Head, Department of Mechanical Engineering, Arunai Engineering College, Tamil Nadu, India
Professor & Head, Department of Automobile Engineering, Karpaga Vinayaga College of Engineering and Technology, Tamil Nadu, India
ABSTRACT Magnesium alloys are the very progressive materials whereon is due to improve their end-use properties. Especially, wrought Mg alloys attract attention since they have more advantageous mechanical properties than cast Mg alloys. Investigations were carried out the effects of heat treatment on tensile strength, hardness and microstructure of AZ61A magnesium alloy. The AZ61A Mg alloy is heat treated at the temperature of 2600C (5000F) and allowed it cool slowly in the furnace itself for various soaking timings such as 120 min, 240 min and 360 minutes as per Stress relief annealing Std., ASTM B557. Magnesium alloys are difficult to predict formability based on its material property and wrought Mg alloy higher strength and ductile compare to cast Mg, due to its HCP structure. So, magnesium alloys are usually heat treated either to improve mechanical properties or as means of conditioning for specific fabrication operations. Special attention had been focused on the analysis of mutual relations existing between the deformation conditions, microstructural parameters and the achieved mechanical properties and finite element analysis is done. The result after solution heat treatment, showed improved tensile strength, 0.2% proof. Strength and remarkably decreased hardness. It would be appropriate for a forming process namely isostatic and Single point incremental forming process.
KEYWORDS: AZ61AMg Alloy, Heat Treatment, Soaking Timing, Tensile Strength, Hardness, Microstructure and Finite Element Analysis
INTRODUCTION Magnesium alloys are widely preferred now a days because of its weight reduction capability and recycling potential. Magnesium alloys are highly suitable for sheet metal forming due to high strain hardening rate (n) and Plastic Strain ratio (r). Thus, the low plasticity at ambient temperatures makes the material difficult for cold working [1]. Magnesium alloys are produced and used in many shapes and forms, i.e., castings, extruded bars, rods, tubing, sheets and plate and forgings [2]. They are suitable for varied stress and non-stress aerospace applications. Their inherent strength, lightweight, shock and vibration resistance are factors which make their use advantageous. The weight for an equal volume of magnesium is approximately two-thirds of that for aluminum and one-fifth of that for steel. The use of magnesium alloys in a variety of technology related applications has seen a progressive growth during the last two decades, and both magnesium and its alloy counterparts continue to make their impact in a spectrum of aerospace industry, automotive products, and military industry [3-4]. Structural applications of magnesium alloys are rapidly increasing in automotive and aerospace equipment due to their low density and high specific strength [5]. In the automotive and aerospace industries, the need to reduce fuel consumption and associated costs has led to the replacement of heavy components with lighter alloys. Moreover, magnesium alloys are 35% lighter than aluminium and possess good machining and casting characteristics.
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S. Thirumalvalavan, R. Senthil & A. Gnanavelbabu
Furthermore, they have excellent specific strength, high elastic modulus and good vibration/damping properties [6]. They are also considered advanced materials in terms of energy conservation and environmental pollution regulations [7]. Nowadays, many researchers made attempt to improve the properties of AZ61A magnesium alloy through heat treatment. For example, Edlira Dhuka et al., [8] studied the Precipitation in Mg alloy AZ61 in dependence of various heat treatments processes. Wang et al., [9] studied the aging process of Mg-Al alloys. MA et al., [10] studied the effect of heat treatment on the microstructure of ZK 60 magnesium alloy. Duly et al., [11] studied the solution process of the Mg-Al alloys. Volkova [12] studied the effect of deformation and heat treatment on the structure and properties of magnesium alloys of the Mg-Zn-Zr system. Guo Feng et al., [13] study on solid solution and aging process of AZ91D magnesium alloy with cerium. Other researchers have investigated and studied about magnesium alloys. Greger et al., [14] studied the possibilities of mechanical properties and microstructure improvement of magnesium alloys. Mohd Ruzi et al., [15] studied a review of workability of wrought magnesium alloys. Yokoyama [16] made an attempt to impact tensile stress-strain characteristics of wrought magnesium alloys. Wang et al., [17] studied on crystal plasticity formability analysis for magnesium alloy sheets. Dobrzanski et al., [18] studied on mechanical properties of magnesium casting alloys. Yuan et al., [19] made an attempt to improve tensile properties and creep resistance of AZ91 alloy containing antimony. However, research efforts on the effect of heat treatment on tensile strength, hardness and microstructure of AZ61A magnesium alloys are rather limited. There seem to be two major problems concerning theses researches on the heat treatment of magnesium alloys; the first is that theses researches fail to touch the optimization of the treatment process of magnesium alloys; and the second is that the mechanical properties of the magnesium alloys proposed above seem to be insufficient for producing high-performance products. Therefore, the objective of the work was to investigate the effect of heat treatment on tensile strength, hardness, microstructure, finite element analysis and formability analysis of AZ61A magnesium alloy, so as to employ the applications of the magnesium alloy components to industrial production.
MATERIALS AND EXPERIMENTAL METHODS Material and Heat Treatment Processes The material used in this study is 6mm thickness AZ61A magnesium alloy plate. Samples of the material were collected and prepared into Chemical, tensile, hardness and metallographic examination specimens. The spectrometric analyses of the magnesium alloy were carried out to determine its chemical composition, and are presented in Table 1. Table 1: Chemical Compositions (wt %) of AZ61A Magnesium Alloy Elements AZ61A Mg alloy
Al 6.4
Zn 0.56
Fe 0.04
Cu 0.02
Ni
