Grain refinement is important for improving the microstructure and mechanical properties of magnesium alloys. Carbon inoculation is an effective method of grain refinement process for magnesium alloys containing aluminum. In this paper, the C2Cl6 and graphite powder were used as the potential grain refiners for AM60 and AZ91 alloys, respectively. The results show that the microstructure and mechanical properties of these Mg-Al magnesium alloys have been improved with these grain refiners. The mechanism and thermodynamics analyses of grain refinement with carbon inoculation in Mg-Al magnesium alloy have been discussed.
An effective dispersion process to cast CNT-reinforced in a concentrated magnesium alloy (AZ31) nanocomposite was investigated in this study. The metal magnesium powder was first coated with dispersed CNTs by wet process, followed by the fabricating of CNT/Mg precursor using mechanical briquetting and extrusion. The resultant precursor was then added into AZ31 alloy during the melting process. Finally, CNT/Mg nanocomposites with grain refinement matrix composite were fabricated in as-cast and as-extruded. Compared with the commercial AZ31 alloy, CNT/Mg nanocomposites exhibited higher yield strength of 270 MPa with an increase of 22.7%, which can be largely ascribed to the effective dispersion process of CNTs in the alloy matrix, and the elongation is no significant decrease.
As a component of servicing car body, the internal interfaces of aluminum alloy carbody include all connections of equipments hanged under floor and mounted on roof, which are expected to form the weak coupling relationship. For an imported prototype with primary hunting phenomenon, a dynamical design methodology of speeding-up bogies was proposed. The analysis graph of full-vehicle stability properties and variation patterns is used to clarify a self-adaptive improvement direction, i.e., λeN ≥ λemin, and λemin = (0.03–0.05). Therefore, the central hollow tread wear can be self-cleaned in time or regularly by crossing over the dedicated lines of different speed-grades. The modified strategy with strong/weak internal interface transaction of servicing car body was furthermore formulated based on the dynamical condensation method of component interface displacements. The causal relationship between bogie vibration alarm and car body fluttering phenomenon was then demonstrated by using techniques of rigid-flex coupling simulation. The self-excited vibration of traction converter intersects with the unstable hunting oscillation, ca. 9.2/9.3 Hz, which is consistent with the conclusions of tracking-test investigations on two car body fluttering formations. The technical space to promote the construction speed is thereby lost completely because of ride comfort decline, unsafe vibration of onboard electrical equipments, and weld fatigue damage of aluminum alloy car body. However, the rigid-flex coupling simulation analyses of trailer TC02/07 confirm that the safety threshold of bogie vibration warning can be appropriately increased as long as the lateral modal frequency of traction converters is greater than 12 Hz, preferably close to 14 Hz.
Abstract. A numerical model was established to investigate the micro hydro-mechanical deep drawing process of austenitic stainless steel 304 foil (0.05 mm thickness). Due to the miniaturisation of the specimen size, the effect of grain size, gap distance and radial pressure during drawing process could be prominent. The results indicate that the appropriate radial pressure and gap distance could improve the limit drawing ratio (LDR) of manufactured cylindrical cups by reducing the friction resistance. The maximum LDR obtained in the present work reaches 3.2, which is much higher than that obtained by conventional deep drawing process.
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