Papers by Keyword: Compression Deformation

Abstract: Effect of intermediate thermomechanical treatment on tensile properties at short-transverse direction, fracture mechanism and microstructure of 2A97 Al-Li alloy thick plate were studied by tensile testing, SEM, EBSD and TEM.The results show that with the increasing of compression deformation, the strength and elongation of the alloy increase first and then decrease slightly. The fracture mode of the alloy changes from quasi-cleavage fracture to high energy ductile fracture. When the compression deformation rises to 20%, the elongated structure are replaced by a more uniform and equiaxial structure. The distribution of δ phase distribute more homogeneously in the grains.

Abstract: The powder sintering process is adopted for preparing the porous Cu-35Ni-15Al alloy.The microstructure was observed by using scanning electron microscopy. Mechanical properties were tested and compared at different temperatures and stress conditions. This thesis also studied the impact of stress on creep properties of Cu-35Ni-15Al alloy,The results show there are roughly three deformation stages of high temperature compression deformation.The microscopic deformation was mainly the curved, collapsed and folded holes.The creep resistance performance of porous Cu-35Ni-15Al alloys weakens with the increasing pressure.

Abstract: The deformation characteristics of pure copper have been investigated by compression tests in the temperature range of 20 °C~900 °C and strain rate range of 0.001 s^-1~1 s^-1. The results showed that the flow stress of pure copper increased with increasing strain rate and decreasing deformation temperature. Three types of strain-contained flow stress prediction models were developed. The flow stress prediction models based on parameters such as α, Q, lnA and n were related to deformation temperature, strain rate and strain, the prediction accuracy of the flow stress was deeply influenced by the cumulative error of multi-parameter fitting. The flow stress prediction model based on σ, , ε and T constitutive relations and the flow stress prediction model based on GA+BP possessed less correlation with microscopic deformation mechanism, proving to have high prediction accuracy, in which GA+ BP-based flow stress prediction model is in very good agreement with true stress curve, which is of significance to the guidance of hot working of pure copper.

Abstract: The semi-solid microstructure evolution of hypereutectic Al-20Si-3Fe-1Mn-4Cu-1Mg alloy was studied by unidirectional compression deformation experiment, at a range of deformation temperature of 833K~873K and a range of strain rate of 0.1s^-1~0.001s^-1. The results showed that the microstructure of the reheating alloy was more spherical and fine than the microstructure of as-cast, the alloy was a positive strain rate sensitive material that the flow stress was decreased with increasing in deformation temperature and it was increased with increasing in strain rate. The mechanical properties of the alloy were hardly improved when the deformation temperature was too high to fracture the thick phase of the alloy.The lower strain rate was not only reducing the productivity but also reducing the plastic deformation. The microstructure of the alloy which the thick phase was broken fundamentally and the grain became further refinement can be obtained at 833K~853K, and at 0.1s^-1~0.01s^-1.It can be done that reducing the plastic deformation resistance and strengthening the fabrication procedure of the alloy.

Abstract: The microstructure, surface morphology, compression properties, deformation behaviour and strain hardening exponent of as-cast and as-extruded AZ31 Mg alloy after different annealing treatments were investigated. The results show that the compression properties are great different between cast AZ31 alloy and extruded AZ31 alloy. Extruded AZ31 alloy is discontinuous yield and on the surface no signs of damage have been observed; on the contrast, cast AZ31 alloy is continuous yield and shows wavy patterns, and the surface cracks can be easily found. In addition, there is a linear relationship between the strain hardening exponent in first deformation stage and the yield ratio. Further more, the twinning mechanism plays very different role in cast AZ31 alloy and extruded AZ31 alloy.

Abstract: Rheological behavior of semi-solid metals during isothermal compression is the most basic forming way for semi-solid die forging. In this paper, based on the metal plastic deformation and high pressure solidification theory, the shear deformation mechanisms of semi-solid metals were analyzed during isothermal compression. Experimental observations and theoretical analyses for AZ91D and composite Al/Al2O3 in the semi-solid state were performed with thermal simulation tests. The results for theoretical analyses and experimental observations show that the shear deformation of semi-solid metals has been realized by metal inhomogeneous flowing from macroscopic view and by grain boundary inhomogeneous migrating from microscopic view respectively during compression.

Abstract: NiAl-based alloy is a promising material applied in the fields of aeronautic and astronautic instruments. In the paper the compression deformation behavior and microstructure evolution of NiAl-Cr(Mo)-Hf alloy at elevated temperature were studied. The results demonstrate that the alloy behaves good formability in the temperature ranging from 1320°C to 1360°C, in which the maximum initial strain rate is about 8.3×10-4s-1 and the maximum deformation resistance is lower than 40MPa. During compression at temperature between 1250°C and 1300°C the flow stress increased sharply with the increasing of the deformation degree. When compression deformation at 1320°C~1360°C, the flow stress decreased obviously and the flow stress decreased slightly after reached the maximum value. By analyzing the microstructure evolution during compression it can be concluded that as-casting microstructure was improved in deformation. The grains were refined and the brittle phases of lamellar Cr(Mo) existing at NiAl matrix were broken. The porosities in as-casting material were eliminated during compression and the density of the material increased. The fracture toughness of the alloy increased from 6.4MPa·m1/2 to 9.8MPa·m1/2 after compression.

Abstract: The effects of rapid solidification on the microstructure and mechanical properties of two kinds of NiAl based eutectics were investigated. Rapid solidification resulted in the following effects, which encompass the refinement of the cell size, lamellar spacing and precipitates, deviation from the equilibrium composition, solubility extension, and a transition from a Heusler phase to an Hf-rich solid solution phase. Except for the deviation from the equilibrium composition, these microstructural characteristics are all beneficial to the improvement of mechanical properties. As a consequence, the room temperature compression yield strength and compression ductility were improved significantly and high temperature strength improved slightly. The high temperature compressive flow behaviour can be described by the temperature-compensated power-law equations.

Abstract: The semi-solid compression deformation behavior of the AZ91D alloy with non-dendritic structure, which was obtained under the semi-solid isothermal treatment condition of 570°C×60min, was studied by means of Gleeble-1500 thermal-mechanical simulator. When the compression strain was lower than 0.7, along with the compression strain increasing, the compression stress firstly increased rapidly, then decreased rapidly, and finally kept a constant stress level gradually. Under the condition of different deformation temperatures and deformation rates, the maximum compression stress was obtained simultaneously when the compression strain value was 0.025 approximatively. Furthermore, when the deformation rate kept a constant, the compression stress decreased along with the deformation temperature increasing, and when the deformation temperature kept a constant, the compression stress increased along with the deformation rate increasing.