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In order to understand the microstructure evolution and the deformation mechanism of medium volume fraction SiCp/Al composite during hot deformation, the hot compression tests of 35 vol%SiCp/2024Al composite were investigated by Gleeble-1500D thermo-mechanical simulators over hot deformation temperatures range of 623–773 K and strain rate of 0.01–10 s−1. The microstructure in different deformation conditions were investigated utilizing OM, SEM and TEM. The results indicated that the flow stress, microstructure evolution, and the deformation mechanism are sensitive to deformation parameters, which can be represented by the Zener-Hollomon parameter (Z) in the hyperbolic sine equation. The softening mechanism, the degree of dynamic recrystallization, the average grain size, the size of precipitates, the dislocation density, and the nucleation mechanism of dynamic recrystallization of the experimental composite is associated with the Z parameter. The specific influence relationships are analyzed, and the interaction laws are obtained.

In this work, the nucleation and growth behavior of Ti2AlC and Ti3AlC nano-precipitates in Ti–44Al–1.2C alloys were systematically studied by observing their distribution, morphology, and interface atomic structure. The experiment results show that the needle-like C atom segregation zones in TiAl alloys are the nucleation site of Ti2AlC, and the long axis direction of segregation zones is parallel to the TiAl(111) plane. The rod-like Ti2AlC nano-precipitates mainly distribute at the TiAl/Ti3Al interface, and the orientation relationship between them is [1̅01\bar{1}01]TiAl//[112̅011\bar{2}0]Ti2AlC//[112̅011\bar{2}0]Ti3Al, (111)TiAl//(0001)Ti2AlC//(0001)Ti3Al. The needle-like Ti3AlC nano-precipitates distribute in TiAl with the orientation relationship of [001]Ti3AlC//[001]TiAl, (100)Ti3AlC//(100)TiAl, (020)Ti3AlC//(020)TiAl, and (110)Ti3AlC//(110)TiAl during the nucleation stage. After growing into the rod-like, the orientation relationship between Ti3AlC precipitates and TiAl is [11̅01\bar{1}0]Ti3AlC//[11̅01\bar{1}0]TiAl, (001)Ti3AlC//(001)TiAl, (220)Ti3AlC//(220)TiAl, and (111)Ti3AlC//(111)TiAl. Both the needle- and rod-like Ti3AlC precipitates preferentially grow along the [001]TiAl direction. The crystal structure and lattice mismatch between Ti2AlC and Ti3AlC nano-precipitates and the TiAl matrix determine their distribution, morphology, and interface atomic structure.

Thermal deformation can improve the properties of aluminum matrix composites (AMCs) prepared by powder metallurgy (P/M) due to the dense and uniform microstructures. And the final microstructure of the AMCs is related to the dynamic recrystallization (DRX) behavior and nucleation mechanism in the thermal forming process. In this regard, the hot compression tests of dual-scale SiC particles reinforced A356 (SiCp/A356) composites prepared by P/M method were carried out at temperatures of 460–520°C and strain rates of 0.01–5 s−1 on a thermal simulation tester. The corresponding microstructure evolution was analyzed by electron back-scattered diffraction and transmission electron microscopy. The results indicated that the stress–strain curve was a typical DRX unimodal stress curve. The comprehensive influences of the strain rate and deformation temperature on the stress were investigated using the Zener–Hollomon parameter (Z), where the deformation activation energy was 443.204 kJ/mol. The DRX critical strain model and DRX volume fraction model were established. DRX behavior of the SiCp/A356 composites was sensitive to the deformation temperatures and strain rates. The micro and nano SiCp can promote the DRX nucleation of Al matrix due to the particle-stimulated nucleation.

This research focuses on the addition of low-cost rare earth metals (REMs) to improve the comprehensive properties of hyper duplex stainless steels (DSSs). The effects of REM on the microstructure, mechanical properties, and pitting corrosion of hyper DSSs were analyzed by optical/scanning electron microscope metallographic examination, X-ray diffraction analysis, tensile test, impact test, and potentiodynamic polarization test. With the addition of REM, micro/nanoscale REM inclusions were formed, and the microstructure of the alloy was refined. With the increasing content of REM, the average diameter and area of inclusions in the alloy decreased at first and then increased. While the mechanical properties showed a trend of first increasing and then decreasing. An appropriate amount of stable REM inclusions could reduce the susceptibility of pitting corrosion and improve the pitting corrosion resistance of the alloy. The hyper DSSs with REM content in the range of 0.018–0.031 wt% have excellent mechanical properties and pitting resistance.

The micromechanical behavior of an Al/Al2Cu/Cu multilayer with characteristic crystal orientation during uniaxial tensile deformation was investigated by molecular dynamics. The simulation results showed that under tensile loading, the dislocation nucleates at the Cu/Al2Cu heterogeneous interface and moves toward the Cu layer along the {111} crystal plane. The deformation mechanism is intralayer confinement slip. As the dislocations proliferated, interactions between them occurred; resulting in the formation of insertion stacking faults and deformation twins in the Cu and Al layers. However, no dislocation lines were generated in the Al2Cu layer during tensile deformation. As the load increased, the stress concentration at the Al2Cu/Al interface led to the fracture of the complex. In addition, the microplastic deformation mechanism and mechanical properties of Al/Al2Cu/Cu composites at different temperatures and strain rates were significantly different. These results revealed the microdeformation mechanism of laminated composites containing brittle phases.

This paper takes nano-SiCp/Al–7Si matrix composites prepared by powder metallurgy as the research object. With the help of advanced microstructure characterization techniques and performance analysis methods, the effect of nano-SiCp volume fraction on the microstructure and properties of composites is systematically studied. Based on optimizing the volume fraction of nano-SiCp, the thermal deformation behavior of the composites is investigated. It was found that with an increase of nano-SiCp content, the distribution uniformity of nano-SiCp decreases gradually. And because the surface of nano-SiCp is easy to adsorb gas and the aggregated distribution of nano-SiCp is not conducive to the sintering process, the density of the composites shows a gradually decreasing trend. The hardness of the composites tends increasing gradually, and the increase in amplitude gradually decreases. Due to the addition of nano-SiCp, there are many interfaces between SiCp and Al matrix, and cracks are prone to initiation and expansion at the interface. Therefore, as the volume fraction of nano-SiCp increases, the elongation of nano-SiCp/Al–7Si composites gradually decreases. When the volume fraction of nano-SiCp is 2%, the strength of the composites reaches the maximum value of 217 MPa. Compared with the Al–Si alloy without adding nano-SiCp, the results increased by 37.3%. In addition, with the decrease of strain rate and the increase of deformation temperature, the dislocation density in the composites gradually decreases, and the dynamic softening progresses more fully. The dynamic recrystallization nucleation mechanism mainly includes the subcrystal merging mechanism and the grain boundary bowing mechanism.

Using the Gleeble-1500D simulator, the high temperature plastic deformation behavior of 40%SiCP/Al-Cu composite were investigated at 350-500℃ with the strain rate of 0.01-10 s-1. The stress-strain curves were obtained during the tests. The critical conditions of dynamic recrystallization for onset of DRX during deformation of 40%SiCP/Al-Cu composite was obtained by computation of the strain hardening rate (θ) from initial stress-strain data and introduction of the inflection point criterion of ln θ-ε curves and the minimum value criterion of (-∂(ln θ)/∂ε)-ε) curves. The results indicate that the softening mechanism of the dynamic recrystallization is a feature of high-temperature flow stress strain curves of the composites, and the peak stress increases with the decrease of deformation temperature or the increase of strain rate. The inflection point in the ln θ-ε curve appears, and the minimum value of the (-∂(ln θ)/∂ε)-ε) curve is presented when the critical state is attained for this composite. The critical strain decreases with the decrease of strain rate and the increase of deformation temperature. There is linear relationship between critical strain and peak strain, i.e. εc=0.528εp. The predicting model of critical strain is described by the function of εc=4.58×10-3Z0.09. Electron microscopic analysis show that the dynamic recrystallization occurs when the strain is 0.06 (T=400℃, ε=10 s-1), and the dynamic recrystallization grains fully grow up when the strain is 0.2.

The aim of this paper was to investigate the effect of vacuum hot pressing sintering temperature, sintering time and pressure on the properties of SiCp/2024Al composites. The microstructures and mechanical properties were tested by scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and a mechanical testing machine. The results indicated that increasing hot pressing temperature decreased the number of pores and increased the density and interfacial bonding strength, and improved the mechanical properties of the composites. The composite fabricated at 580°C exhibited the optimum tensile strength, excessive hot pressing temperature easily produced micro-cracks, and the liquid aluminum extrusion and the reduction of Al2 Cu phase. Prolonged sintering times had an adverse effect on the strength of the composite. A hot vacuum pressure needed to be higher than 60 MPa to achieve densification of composites above 99%. Solution treatment plus aging of the composites resulted in a significant improvement in strength and hardness. The higher the sintering temperature, the shorter the time taken to achieve the hardness peak.

In the present study, the tested hypereutectic Al-21wt.%Si alloys were prepared by modifying the melt using different proportions of P and Ce, and then applying T6 heat treatment. The modification effects and mechanism of P+Ce complex modifier on the Si phase of hypereutectic Al-21wt.%Si alloy were studied, and the aging precipitation behavior after modification was characterized by means of tensile strength measurement, OM, SEM and TEM analysis. The results show that the massive primary silicon phase particles are significantly refined after modification, while the needle-like eutectic silicon crystals become fibrous and short. It was found that the mechanism of phosphorus modification on the primary silicon can be attributed to heterogeneous nucleation of AlP, while the modification mechanism of Ce can be explained by adsorbing-twinning theory. In the aged microstructure of the modified hypereutectic Al-21wt.%Si alloy, there existed some strengthening phases such as Al4Cu9, Al2Cu, AlCu3, and Al57Mn12. The P+Ce complex modifier not only affected the size of primary silicon and eutectic silicon, but also the aging behavior of alloys under the heat treatment process. When Al-21wt.%Si alloy was modified using 0.08%wt.P + 0.6wt.% Ce, the aging precipitates were dispersed uniformly in the alloy, and its mechanical properties at room and elevated temperatures are optimized (Rm = 287.6 MPa at RT, Rm = 210 MPa at 300 ℃).

The infl uence of non-metallic inclusions on quality and performance of steel depends on not only the quantity of inclusions, but also the type, shape, size, distribution, and deformation behavior. In this paper, ANSYS fi nite element analysis software is used to simulate the stress fi eld of inclusions appearing in heavy rudder arm steel castings, the effects of inclusion type, shape, distribution, and various loading conditions were studied. The micromechanics of inclusions in such castings were also analyzed. Such research provides further clarifi cation on reaction mechanism of inclusions under complex loading conditions.

The wear resistance of six kinds of the electrolytic low-titanium eutectic Al-Si piston alloys with various Ti content ranging from 0.00wt.% to 0.21wt.% has been studied. A new method of adding Ti is adopted in the electrolytic low-titanium aluminum alloy ingots. The electrolytic low-titanium eutectic Al-Si piston alloys are produced by remelting the electrolytic low-titanium aluminum alloy, crystal silicon, pure magnesium, Al-50%Cu and Al-10%Mn master alloy. The wear experiments are conducted using MM200 wear testing machine under lubricating condition. The results indicate that the better wear resistance and the less weight loss are achieved in the study for the eutectic Al-Si piston alloys with 0.08wt.%–0.12wt.% Ti content. The highest ultimate tensile strength of 135.94 MPa at 300℃ and HV141.70 hardness of the alloys are obtained at 0.12wt.% and 0.08wt.% Ti content, respectively. The wear mechanism of the eutectic Al-Si piston alloys under lubricating condition is abrasive wear.