Internal friction and microplastic deformation behavior of pure magnesium processed by equal channel angular pressing

Abstract

a b s t r a c tEqual channel angular pressing (ECAP) was performed on the as-extruded commercial pure magnesium at 250 1C for 4 passes. The internal friction of the ECAPed pure Mg as a function of strain amplitude was investigated by dynamic mechanical analyzer (DMA), and the cyclic microplasticity of pure Mg was investigated by tensile loading and unloading test. After ECAP processing, the grain size is significantly refined, the texture component with basal planes parallel to extrusion direction is replaced by a new stronger one with basal planes having a tilting angle of about 401 to the extrusion direction. The stress in microplastic region is reduced with increasing ECAP passes, while the internal friction increases. The internal friction of Mg at high strain amplitude is closely related to microplastic deformation and can be interpreted by dislocation mechanism. The Granato and Lücke model only satisfies in anelastic regions, while the internal friction in microplastic deformation region should be explained in terms of the internal friction model postulated by Peguin. The internal friction related to microplasticity can be divided into two parts with different activation volumes of dislocation motion, which correspond to the two regions of microplasctic deformation process. The initial stage associated with dislocation motion on basal plane shows larger activation volume and lower friction stress of dislocations. The second stage related to the annihilation and tangle of dislocations is characterized by larger hardening exponent and friction stress.

Internal Friction in Magnesium Alloys and Magnesium Alloys- Based Composites

“…One relaxation peak found at 490 K was attributed to the grain boundary sliding. Similar results of polycrystalline magnesium and magnesium alloys were found by several authors [5][6][7][8][9][10][11]. Internal friction peaks measured at low temperatures in magnesium by Fantozzi et al [12] and Seyed Reihani et al [13] were attributed to the so-called Bordoni relaxation, that is, the intrinsic mobility of dislocations through the Peierls barriers.…”

“…(8), the δ H component of decrement depends exponentially on the stress amplitude. The experimental curves were fitted according to formula (8) in the form…”

“…Ageing effects in magnesium alloys were studied using ADIF [17,18] and also TDIF [19]. The influence of microplastic and cyclic deformation on the damping capacity was studied in Mg and Mg alloys using ADIF [8,20,21]. Formation of new interfaces in magnesium alloys via precipitation [22], mechanical twinning [23] or an adding of ceramic particles or fibres [24,25]…”

Effect of grain and secondary phase morphologies in the mechanical and damping behavior of Al7075 alloys

“…(2) Low values of strain, imply a value of internal friction that is strain independent and assumes the value of δ 0 , as a result of reversible movements of dislocation and microscopic yielding around the initial pinned positions [14], and is associated to the values obtained by the application of Eq. (3) [15]. Where ρ is the dislocation density and L d is the mean length of dislocation between the weak pinning points.…”

Effect of Ultrasonic Treatment in the Static and Dynamic Mechanical Behavior of AZ91D Mg Alloy

“…If the strain amplitude values are increase, higher than the material critical strain (εcr), the internal friction becomes strain-dependent and increases exponentially. The strain-independent internal friction is the result of reversible movements of dislocation and microscopic yielding [14] around the initial pinned positions and is associated to the values obtained by the application of Equation (8) (8) where ρ is the dislocation density and l is the mean length of dislocation between the weak pinning points [15]. Dislocation damping can be enhanced by thermal activation.…”