Abstract: This Magnesium (Mg) alloys have been increasingly used in the automotive industry due to their superior mechanical properties compared with other metals. While there are some obstacles in the application of Mg alloy, one of that is its complex dynamic response characteristic. Many papers have studied the tensile and compression properties of AZ31B Mg alloys sheet, but lack of shear test. This paper presents experimental study, including the test method and test data analysis, on the AZ31B Mg alloy sheet. Uniaxial tension tests were carried out over a wide range of strain rates from to , which are of interest in vehicle crash CAE. At the same time uniaxial compression and shear tests at strain rates from to were also carried out. The different mechanical behavior of AZ31B Mg alloys sheet between tensile, compression and shear stress states can also be studied in this paper.
Abstract: In this paper, first, based on the employing environment and properties requirement of offshore platform, the influence of various alloying elements on the performance of steel was analyzed and chemical composition of a new ultra-high-strength alloy steel was designed. Then, the designed alloy steel specimen has been prepared using intermediate frequency induction furnace. Austenization temperature of the steel was determined through thermal dilatometer. The effects of quenching and tempering process on microstructure and mechanical properties of the steel were studied by means of optical microscopy (OM), scanning electron microscopy (SEM), durometer and universal material tensile tester. The research results indicated that the casting microstructure of the designed steel was a duplex structure of martensite and acicular bainite. The austenitizing onset temperature (Ac1) and termination temperature (Ac3) was 700°C and 790°C, respectively. With the increase of the austenitizing temperature, the hardness of the steel first increased until it reached the maximum value at 860°C and then decreased above 860°C. Meanwhile, the hardness of the steel decreased with the increasing of the tempering temperature in the range 150°C-500°C. The optimal heat-treatment processes were concluded as follows: heating up to 860°C, quenching by oil, and then tempering at 170°C. The superior mechanical properties of tensile strength of 1400MPa and elongation of 6.5% as well as the microstructure of tempered martensite were obtained after this heat treatment.
Abstract: This work reports the result of heat treatment on microstructures and mechanical property of ZA-27 zinc alloy gear part produced by a slurry squeeze casting process. The Gas Induced Semi-Solid (GISS) technique was employed for preparation of the alloy slurry. The microstructures and mechanical property of the alloy were studied by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and HRB hardness testing. The specimens were solid solution heat treated at 365 °C for 1 h and artificially aged at 150 °C for 0.5, 1, 3, 6, 12 and 24 h. The as-cast microstructures of the alloy mainly consist of globular primary α phase surrounded by β, η and ε phases. After solution treatment the primary α and η phases were dissolved and transformed to the supersaturated β phase. At the early stage of ageing (0.5 – 3 h) the β phase decomposed to α and η phases. After a long period of ageing (6 – 24 h) α and ε phases decomposed through the transformation reaction: α + ε → T’+η. The hardness of specimens was increased after ageing for 0.5 h and gradually decreased with increasing ageing time. The peak hardness was 82 HRB at 0.5 h ageing. The hardness decreased to 62 HRB after ageing for 24 h.
Abstract: This research focused on the effect of solution heat treated microstructures on anodic oxide formations of casting 7075 Al alloy. The casting specimens were solution heat treated at 450°C for various holding. The results showed that the quality of anodic oxide film on the specimen with 4h solution heat treatment time was higher than that of at other conditions. Because its microstructures obtained the lowest amounts of secondary phase particles leading to improve the quality of oxide film and also reduce defects in oxide film. On the other hand, coarse black particles of Mg2Si formed increasingly in microstructures of specimens after solution treatment at prolong holding time of 8h and 16h resulted in discontinues oxide films forming on them.
Abstract: The effect of B and Cr on hardenability in 0.33% C cold heading steel was studied. The results show that the hardenability enhanced from adding 0.0020% B or 0.28% Cr. The length of high hardness stability region of the Jominy Curve obviously increased with adding B,and the hardness of low hardness stability region of the Jominy Curve increased significantly with adding Cr. The ideal critical diameter DI of the experimental steels was calculated, the DI is 20.0 mm of the base steel with 0.33% C and no other alloying element addition, but the DI becomes 29.5 mm with adding 0.28% Cr and 46.4mm with adding 0.0020% B. The hardenability of the test steels was calculated by the nonlinear equation and compared with the experimental results. The calculated Jominy curve did not reflect characteristics of 2# steel with B and needs to be further optimized.
Abstract: The dynamic compressive mechanical behavior of railway wheel steel at room temperature was investigated experimentally for strain rates up to ~2300/s, by using a split Hopkinson pressure bar (SHPB) apparatus. Experimental results indicate that the wheel steel exhibits an obvious strain rate-dependence; both yield strength and flow stress enhance with the increase of strain rate. Based on experimental data, an empirical dynamic constitutive model was used to describe the strain rate effect of wheel steel. These research results could provide reliable and accurate material constitutive parameters for wheel-rail impact simulations, to guide the design and assessment of the safety of the wheel-rail system.
Abstract: The modifiers of nano-SiC and nano-TiN were added into the melt of ZGMn13Cr2 alloy, respectively. The effect of the additions on the microstructure and mechanical properties were investigated. Results show that the two kinds of nano modifiers both have refining effect and make the improvement of impact toughness and wear resistance.
Abstract: Notch fatigue behavior of Ti-6Al-4V titanium alloy has been investigated under a load-controlled high cycle fatigue test. The S-N curve was kinked at the critical nominal stress amplitude, where the plastic deformation nucleated at notch root. The plastic zone size at the critical nominal stress amplitude was almost equal to the size of 4 grains of the present Ti-6Al-4V alloy, which were the same findings as in the 2024-T4 alloy used in the previous study. Above the critical nominal stress amplitude, the local stress ratio at notch root decreased with increasing nominal stress amplitude. The critical nominal stress amplitudes normalized by the cyclic yield stress were almost the same for Ti-6Al-4V alloy and the 2024-T4 alloy. The significant decrease of the local stress ratio with increasing nominal stress amplitude was observed in the 2024-T4 alloy with low cyclic yield stress and low cyclic hardening coefficient compared to the Ti-6Al-4V alloy with high cyclic yield stress and high cyclic hardening coefficient.
Abstract: A new continuous annealing process which can eliminate the "band" feature of dual phase steels has been designed. The sheets were annealed in MULTIPAS annealing simulator under variation of annealing temperature. The microstructure evolution of dual-phase steel sheets annealed at intercritical temperatures, were analyzed by optical microscopy and scanning electron microscopy. And the properties were compared with the sheets which annealed by the existing annealing process. The results show that: the "band" feature of dual-phase steel can be effectively eliminated by the optimizing continuous annealing process,and the mechanical properties are improved.