Iram Raza Ahmad

Tensile Properties of Die-Cast Magnesium Alloy AZ91D at High Strain Rates in the Range between 300 s-1 and 1500 s-1

Magnesium alloys have been increasingly used in the automobile, aerospace and communication industries due to their low density, high strength to weight ratio, good impact resistance and castability. Magnesium alloys, previously not used in load bearing components and structural parts are strongly being considered for use in such applications. Impact events in vehicles and airplanes as well as developments in weaponry and high speed metal working are all characterized by high rates of loading. Understanding of the dynamic behaviour of materials is critical for proper design and use in different applications. In the current study, a cast magnesium alloy AZ91D has been investigated at quasi-static and higher strain rates in the range between 300 s-1 and 1500 s-1. The INSTRON machine was used to perform the quasi-static tests. High strain rate tests have been performed using the Split Hopkinson Tensile Bar (SHTB), a very useful and widely used tool to study the dynamic behaviour of variety of engineering materials. The results of a tensile testing indicate that the tensile properties including yield strength (YS), ultimate tensile strength (UTS) and the elongation at fracture (Ef) are affected by the strain rate variation. Higher stresses are associated with higher strain rates. The alloy AZ91D displays approximately 45% higher tensile stresses at an average strain rate of approximately 1215/s than at quasi-static strain rate. The dependence of the yield stress and tensile strength on the strain rate in the range of high strain rate above 1000 s-1 is larger than that at lower strain rates. The alloy AZ91D is observed to be more strain rate sensitive for strain rate higher than 1000 s-1. A decrease in the strain rate sensitivity is also observed with the increasing strain in the specimen. It is observed that the hardening behaviour of the alloy is affected with increasing the strain rate. At high strain rates, the fracture of magnesium alloy AZ91D tends to transit from ductile to brittle.

Magnesium Alloys: An Alternative for Aluminium in Structural Applications

There is a fast moving trend towards using lightweight materials in automotive, aerospace, building and construction, body armour and protection, sports and leisure goods. The dynamic industrial development puts higher demands for lighter and yet stronger materials. Magnesium alloys potentially met the present demands for lighter and reliable construction. With comparable specific stiffness, higher specific strength and energy absorption magnesium alloys have the potential to replace steel and aluminum alloys. Magnesium alloys are very useful for applications where materials are subjected to variable or dynamic loads such as crash events in vehicles and planes, buildings and structures against projectiles penetration etc. To know the materials’ response to impacts and their resistance to blast and shock, it is necessary to understand their behaviour under static as well as dynamic conditions. In current study, magnesium alloys AZ91D and AM50 have been studied at dynamic loading conditions and compared with aluminum alloy AA6061-T6. With significant mass saving, higher specific properties and higher energy absorption under dynamic loadings, magnesium alloys are promising candidates to replace conventional materials not only aluminum but steel as well in structural applications.

Experimental and Constitutive Study of Tensile Behavior of AZ31B Wrought Magnesium Alloy

AbstractAutomotive and aerospace manufacturers are looking for ways to reduce the gross weight of vehicles to economize on fuel consumption as well as improve performance. Magnesium alloys, being the lightest among the metals, are highly attractive as potential structural materials. However, their use is quite limited, especially in structural applications. As of this writing, knowledge of the dynamic behavior of magnesium alloys is not sufficient to depict their true response under dynamic loadings, and has been a hindrance to their widespread use. In this research, an experimental study, followed by constitutive and microstructural analyses, was carried out to investigate the behavior of AZ31B magnesium alloy. The alloy has been tested at strain rates in the range between 10−4 s−1 and 1.5×103 s−1 under tension.

Dynamic Response of Magnesium Alloy AZ31B under High Strain Rate Compressive Loading

Magnesium alloys have been increasingly used in automobile, aerospace, consumer electronics and communication industries due to their low density, high strength to weight ratio, good impact resistance and castability. Impact situations in vehicles and airplanes and high speed metal working are characterized with the high rates of loading. The dynamic properties of materials are critical to evaluate the materials’ response in impact situations. They are also useful to design various automotive and aerospace components that are subjected to high rates of loadings. In current study, the compressive behaviour of magnesium alloy AZ31B has been examined over a wide range of strain rate between 103 and 3x103 s-1 in order to evaluate its potential in structural applications. Higher stresses are observed at higher strain rates. The peak stress increases about 10% for an increase in the strain rate from 980 s-1 to 2450 s-1. The hardening exponent n increases from 0.65 to 0.72 with increasing strain rate from 980 s-1 to 2450 s-1 indicating that the alloy is rate sensitive. However, the rate sensitivity of the alloy is negligible at lower strains and is significantly higher at higher strains. Energy absorption during deformation in general is increased with the strain rate.

Strain Rate Effect on Microstructure of Dynamically Compressed Magnesium Alloy AZ31B

Lightweight materials have been in focus in recent times for their use in automobiles, planes and protective structures for numerous benefits ranging from reduction in fuel consumption and increased payload in vehicles to lighter and stronger protective structures. For efficient use of materials in applications where they are subjected to unusual higher sudden loads, it is necessary to understand their mechanical behaviour under such conditions.In present study, the effect of strain rate on deformation of magnesium alloy AZ31Bunder compression has been investigated. The alloy is subjected to various strain rates as 10-4s-1, 500s-1 and 2500s-1 and the microstructural analysis was performed to see the changes in the microstructure of the alloy and their effect on the mechanical response of the alloy is portrayed.

Effect of Temperature on the Dynamic Compressive Properties of Magnesium Alloy AZ91D

Lightweight materials are getting more and more attraction towards their use in automobiles, planes, protective structures, electronics and supports for numerous benefits ranging from reduction in fuel consumption in vehicles to lighter and stronger in protective structures. For efficient use of materials in applications where they are subjected to unusual higher sudden loads and varying temperatures, it is necessary to know their accurate response under such conditions. Magnesium alloys due to low density, high specific strength, high specific stiffness and damping capacity have been in use for variety of structural and non-structural applications mainly in automotive and aerospace industries along with many other applications in defense, supports and electronics. In present study, the effect of temperature variation has been investigated for magnesium alloy AZ91D at high strain rates. The temperature is varied in the range between -30oC to 200oC at a strain rate of 103 s-1. Lower stresses and larger strains to peak compressive stresses are observed with increasing temperature. At higher strain rate, the effect of temperature on the alloy’s hardening behaviour is less significant

Magnesium Alloys a Promising Option as Protection Materials

Lighter yet stronger magnesium alloys have become very attractive for applications where materials undergo larger strains such as crash events in vehicles and planes, penetration of projectiles in personal body armour and vehicle armours. Excellent combination of light weight and good mechanical properties put magnesium alloys ahead of other structural materials in applications where high specific properties are required. It is well anticipated that magnesium alloys have enormous potential as a whole or a part of protective structures.

Anisotropic Behaviour of AZ31B Sheet at High Strain Rates

The anisotropic effects on the mechanical response of AZ31B sheet at high strain rates have been analyzed. The experimental results indicate that the stress-strain behaviour of the alloy is highly anisotropic and rate sensitive. However, anisotropy of the mechanical properties of the alloy is less significant at higher strain rates. Under tensile loading, the anisotropic behaviour of the alloy is less significant as compare to its behaviour under compression. In both compression and tensile loading the alloy shows significant rate sensitivity as compare to quasi-static strain rates but at higher rates it is less significant. The maximum stress is observed to reach nearly 600 MPa for transverse direction impact. The tension-compression asymmetry is observed in the alloy.

Effect of Specimen Dimensions in Dynamic Torsion Testing

The effect of specimen’s mean radius to average wall-thickness ratio rs/t, has been studied using the Split Hopkinson Torsional Bar. The rs/t ratio was varied between 6.5 and 39 keeping the outer diameter and the gauge length of the specimen constant. Higher strain rates and strains are observed for specimens with larger specimen radius to wall-thickness ratio rs/t. However no monotonic trend of the shear stress with rs/t variation is found. A sharp decrease in the torsional stiffness of the specimen is observed with increasing the specimen’s rs/t ratio. The rs/t ratio can also be used as a useful dimension to enhance the strain rate in tubular specimens.