N. Prabhu

Grain Growth and β-Mg17Al12 Intermetallic Phase Dissolution During Heat Treatment and Its Impact on Deformation Behavior of AZ80 Mg-Alloy

Microstructure evolution after solutionizing and ageing treatment of cast AZ80 Mg alloy were investigated using optical and scanning electron microscopy. Effect of these treatments on grain size, β-Mg17Al12 intermetallic phase, mechanical behavior, and flow asymmetry were investigated. The initial continuous network of β-phase found to be reduced after solutionizing. The dissolution of β-phase and simultaneous grain growth are found to be interrelated. Mechanical properties including yield strength, maximum strength (ultimate compressive strength), and maximum strain attainable in compressive found almost twice than the corresponding values obtained in tension. The asymmetry in compressive and tensile properties is found to decrease with grain size at certain solutionizing duration. Particular heat treatment found to offer best combination of tensile compressive flow properties in AZ80 Mg alloy. Aging under certain conditions found to minimize the strength asymmetry.

Effect of High Temperature Caliber Rolling on Microstructure and Room Temperature Tensile Properties of Mg-3Al-1Zn (AZ31) Alloy

Mg-3Al-1Zn (AZ31) alloy was caliber rolled at 250, 300, 350, 400 and 450 °C. The effects of caliber rolling temperature on the microstructure and tensile properties were investigated. The room temperature tensile tests were carried out to failure at a strain rate of 1 x 10 -4 s-1. The nature of stress-strain curves obtained was found to vary with the temperature employed in caliber rolling. The yield strength and tensile strength followed a sinusoidal behaviour with increasing caliber rolling temperature but no such trend was noted in ductility. These variations in tensile properties were explained by the varying grain sizes obtained as a function of caliber rolling temperature.

Effect of Severe Caliber Rolling on Superplastic Properties of Mg-3Al-1Zn (AZ31) Alloy

Fine grains were developed in Mg-3Al-1Zn (AZ31) alloy by isothermal caliber rolling at five different temperatures in the range of 250-450°C. The samples of different grain sizes were deformed by constant strain rate and differential strain rate test techniques over the temperature range of 220-450 °C and strain rate range of 10-5 to 10-1 s-1. The effects of grain size, test temperature and strain rate on flow stSuperscSuperscript textript textress were analysed to develop the constitutive relationship for supSuperscript texterplastic deformation. The parameters of the constitutive relationship obtained from the constant strain rate tests and differential strain rate tests were used to find out the material constant A of the constitutive relationship.

Effects of temperature and strain rate on compressive flow behavior of aluminum-boron carbide composites

Flow properties of aluminum and aluminum-boron carbide (Al-B4C) composites, containing 5, 10 and 15 wt% B4C, were investigated by compression tests at strain rates of 10−4, 10−3 and 10−2 s−1 over the temperature range 25 to 500℃. The nature of stress–strain curves as a function of reinforcement, temperature and strain rate revealed that (1) flow stress initially increases as the reinforcement increases, but it decreases for Al-15% B4C composite, (2) flow stress increases with the increase in strain rate, with the strain rate sensitivity index varying from 0.01 for aluminum at 200℃ to 0.30 for Al-5% B4C composite. The activation energy for deformation is found to vary from 124 to 187 kJ/mol for Al-15% B4C and Al-5% B4C composites, respectively.

On the High Temperature Deformation Behaviour of 2507 Super Duplex Stainless Steel

High temperature deformation behaviour of 2507 super duplex stainless steel was investigated by conducting isothermal hot compression tests. The dominant restoration processes in ferrite and austenite phases present in the material were found to be distinct. The possible causes for these differences are discussed. Based on the dynamic materials model, processing map was developed to identify the optimum processing parameters. The microstructural mechanisms operating in the material were identified. A unified strain-compensated constitutive equation was established to describe the high temperature deformation behaviour of the material under the identified processing conditions. Standard statistical parameter such as correlation coefficient has been used to validate the established equation.

Effect of Rolling on Microstructure and Room Temperature Tensile Properties of Newly Developed Mg-4Li-1Ca Alloy

Mg-30Ca and Mg-14Li (wt %) master alloys were melted successively in the induction furnace to obtain a Mg-Li-Ca ternary alloy containing 3.99 % Li and 1 % Ca. The as-cast material of thickness 4 mm was homogenised at 350° C for 120 mins and subsequently rolled to 62.5 % reduction in thickness at 300 °C to get 1.5 mm thick sheet. The microstructures of hot rolled samples were examined in as-rolled condition as well as after annealing at 350° C for various lengths of time. The presence of deformation twins was clearly seen in the as-rolled structure, whereas equiaxed twin-free grains were observed in the annealed condition. The average grain size was found to increase from 10 μm to 18 μm by annealing, according to the kinetics that follows a parabolic law. Tensile samples taken from rolled plate were deformed to failure at room temperature and a strain rate of 10-4 s-1. Ultimate tensile strength of as-rolled material increased to 213 MPa, while tensile elongation dropped to 6.5 % from the initial values of 134 MPa and 8.5 %, respectively. Annealing after rolling offered a good compromise between the enhanced tensile strength (160 MPa) and tensile ductility (9 %) suggesting viability of the proposed thermomechanical treatment as a means for enhancing both strength and ductility of Mg-4Li-1Ca alloy.

Friction Stir Processing of 2507 Super Duplex Stainless Steel: Microstructure and Corrosion Behaviour

Friction stir processing (FSP) has been shown to be effective in the microstructural modification. In this study, 2507 super duplex stainless steel was subjected to multipass FSP and the processed samples were investigated. Refinement in grain size of both ferrite and austenite was observed in the stir zone of the processed samples. Increased number of passes led to further reduction in grain size. Anodic polarization studies in 3.5 wt% NaCl solution showed that the processed samples possessed improved corrosion resistance. The Mott-Schottky analysis confirmed that the charge carrier density in the passive oxide layer is decreased with decreasing grain size.

Comparison of flow behavior of as-cast and hot rolled Al-B4C composites by constant and differential strain rate tests

High temperature tensile flow behavior of aluminum-boron carbide (Al-B4C) composites of 0, 5 and 15% B4C, hot rolled to ~88% with intermediate annealing at 350 °C, was investigated by constant initial strain rate (CIS) test technique at 500 °C and strain rate jump test technique over the temperature range of 400–500 °C. In the as-cast condition, the flow stresses obtained between CIS and strain rate jump test techniques were found to be significantly different at 500 °C. The strain rate sensitivity index (m) was found to be ~0.1 over for all the composites in both as-cast as well as hot rolled condition. Tensile elongations were found to be 0.36 in both as-cast and hot rolled aluminum, whereas the same reduced in Al-5% B4C composite to 0.35 and 0.27, respectively. The values of activation energy (Q) for deformation of rolled aluminum and Al-5% B4C composite were determined to be 194.2 and 73.4 kJ/mol, respectively. The microstructural examination, using SEM and EBSD techniques, revealed cavitation in aluminum upon differential strain rate test, and grain refinement upon rolling, which increased later during tensile test.

Effect of Annealing on Hardness Penetration of Caliber Rolled Mg-3Al-1Zn (AZ31) Alloy

– Mg-3Al-1Zn (AZ31) alloy was caliber rolled isothermally at the temperature of 300 °C to develop fine grains of 3.6 μm. Annealing was carried out at various times and temperatures. Along with microstructure, annealing affects the hardness and hardness penetration depth. The hardness penetration depth of caliber rolled bar during annealing at 300 to 450 °C was investigated for 5 to 60 minutes. The change in hardness penetration depth were analysed and the mechanisms involved were discussed.

Kinetics of γ-Mg17Al12 Phase Dissolution and its Effect on Room Temperature Tensile Properties in As-Cast AZ80 Magnesium Alloy

As-cast AZ80 magnesium alloy consists of α-Mg, eutectic product of α-Mg and γ-Mg17Al12, with the latter present in the form of partially and fully divorce eutectic. There occurs dissolution of harder γ-Mg17Al12 phase during homogenization treatment at 400 ᵒ and 439 ᵒC. The proportion of the α-Mg and γ-Mg17Al12 phase was varied by solutionizing the alloy for various lengths of time at these temperatures, in order to investigate the kinetics of phase transformation and to evaluate the effect of phase proportion, size and morphology on room temperature tensile properties. It was found that the yield strength decreases with the increase in solutionizing temperature from 400ᵒ to 439 ᵒC and at the same time, ductility in general increases with the increasing solutionizing temperature. The variation in tensile properties and the nature of fractographs were analyzed in terms of the effects of microstructure