Papers by Keyword: Al₄C₃

Abstract: This article reports the effect of MnCO₃ addition on the grain refinement efficiency of AZ91 magnesium alloy. The results indicate that the addition of MnCO₃ has excellent grain refining efficiency for AZ91 alloy, which is mainly attributed to the Al₄C₃ particles formed in the melt, besides Mn is indispensable to grain refinement in Al-bearing magnesium alloys. There is an optimal addition amount of 0.6% at 740 °C and the grain size is reduced from 245 to 91 μm. At the same time, the corrosion resistance performance of MnCO₃-added AZ91is improved.

Abstract: Formation mechanism of TiC in Al matrix at a rather low melting temperature using in situ technology was studied. And effect of the melting temperature on the microstructure of in-situ TiC/Al composite was investigated. The results indicate that, the resultants of TiC and Al₃Ti were found out in the matrix; however, no evidence showed that Al₄C₃, a resultant phase existed probably in TiC/Al composite in accordance with the relative reference, was found out. Compared to the sample of T750, more TiC and less Al₃Ti existed in the sample of T850, and morphography of Al₃Ti changed from block to bar with the increasing melting temperature. The melting temperature affected extremely the reaction speed and the resultants.

Abstract: This paper presents results of the microstructure characterization and evaluation of physical and mechanical properties of Al/SiC_p composites intentionally containing the Al₄C₃ phase prepared by pressureless infiltration, as well as results of treating the composites by the hybrid system chemical vapor deposition (HYSYCVD) route using Na₂SiF₆ as solid precursor. It also contains thermodynamic feasibility calculations (using the HSC 6.1^TM program) of possible reactions between the SiF_{x (x=1-4)} gas species (produced during the thermal decomposition of Na₂SiF₆), Al₄C₃ and N₂ in the atmosphere. The composites were fabricated using an L4 Taguchi experimental design, infiltrating SiC_p porous preforms at 1100 and 1200 °C in ultra high purity (UHP) argon and nitrogen (ArN₂) atmosphere for 90 and 120 min, with the Al-6Si-16Mg (wt. %) alloy. The specimens were characterized by XRD, SEM and EDS. Results show that the composites exhibit a surface hardness between 63.95 and 86.5 (HR30T) and Young´s modulus up to 118.2 GPa. Application of a post-processing stage by HYSYCVD led to the elimination of Al₄C₃ and the formation of a coating of stable phases on the composites surface. The experimental results confirm the thermodynamic feasibility of the proposed chemical reactions.

Abstract: The effects of electromagnetic stirring and Al₄C₃ grain refiner on the grain refinement of semi-continuously cast AZ31 magnesium alloy were discussed in this investigation. The results indicate that electromagnetic stirring has effective refining effect on the grain size of AZ31 magnesium alloy under the effect of Al₄C₃ grain refiner. Electromagnetic stirring can “activate” the Al₄C₃ particles, resulting in more heterogeneous nucleation sites for the primary α-Mg grains. But, longer holding time can “inactivate” the Al₄C₃ particles, and the optimal experimental holding time is 60 min in the present investigation. The activated rate of the electromagnetic under the experimental condition ρ2=1.65%.

Abstract: Experiments were conducted to fabricate the Al₄C3 particles by powder in-situ synthesis process under argon atmosphere and examine the grain refinement of AZ91D magnesium alloy with the addition of 0.6%Al₄C₃(hereafter in mass fraction,%). By means of X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS), the results show the successful fabrication of Al₄C₃ particles. After adding 0.6%Al₄C₃, the average grain size of AZ91D magnesium alloy decreased from 360μm to 243μm. Based on the differential thermal analysis (DTA) results and calculations of the planar disregistry between Al₄C3 and α-Mg, Al₄C3 particles located in the central regions of magnesium grains can act as the heterogeneous nucleus of primary α-Mg phase.

Abstract: Heterogeneous nucleation is a critical factor for grain refinement magnesium alloys. The paper reports the Al-9wt.%Mg-10wt.%SiCp master alloy were prepared by adding SiCp into the Al-Mg molten with stirring in 610-595°C, which were introduced into AZ91. Experimental results indicated Al4C3 were in situ synthesis on the surface of SiCp by the reaction between SiCp and Al in 850°C, which could be as nucleant substrate for primary Mg during the solildification of magnesium alloys. This investigation provided a novel idea for grain refinement Mg-Al alloy.

Abstract: In the present study highly dense (open porosity < 1 %), light-weight (d £ 2.85 g/cm3) and Al4C3-free non-oxide ceramic-metal composites were produced at comparatively low temperatures ( 1250°C) by pressurless melt infiltration. Phase analysis of the SiC-B4C-Al composites revealed that a significant amount of hygroscopic Al4SiC4 and Al4C3 phases were formed. Si3N4 powder was added in different amounts to the SiC-B4C powder batches to suppress formation of these phases via in-situ reactions during the infiltration process. X-ray diffraction results of the SiC-B4C-Si3N4-Al composites confirmed that the incorporation of Si3N4 to the SiC-B4C system reduced or eliminated the formation of the hygroscopic phases and resulted in in-situ formation of AlN, SiC and Si phases in the composite.

Abstract: Al/Ti3SiC2 composite samples were prepared by pressless-sintering route with high purity of polycrystalline Ti3SiC2 and aluminum powders. As yttria Y2O3 being additives during sintering process, the interesting change is that impurities Al4C3, Al4SiC4 and Al3Ti phase which are familiar in products of reactions between Ti3SiC2 and aluminum disappeared and that is valuable to stability of Al/Ti3SiC2 composite in atmosphere due to hydrolyzation of Al4C3. Then the tribological properties of 50Al/ 45Ti3SiC2/5Y2O3 and 50Al/50Ti3SiC2 were investigated by sliding the composites block dryly against low carbon steel disk for the sliding speed 20 m/s and the normal pressure of 0.2~0.8MPa. It was found that with load higher, the friction coefficient of 50Al/45Ti3SiC2/5Y2O3 increased from 0.21 to 0.57 and then reduced to 0.48, which is a little higher than 50Al/50Ti3SiC2 on large scale of pressure except under 0.2 ~ 0.3 MPa, but meanwhile it is remarkable that its rate of wear maintained a nearly steady value about 1.40 × 10-5 mm3/N·m comparing with 50Al/50Ti3SiC2, which shows a valuable tribological properties called non-pressure dependence to frictional materials.

Abstract: Additions of grain refiners based on Ca, Ca/Si, Al3Ti and Al4C3 to pure magnesium and AZ31 alloy result in remarkable microstructure refinement. With proper amount of these refiners addition, the grain size in as-cast ingots is one order of magnitude lower than that without refiner addition. Small amount of refiner addition to alloy AZ31 increases both ultimate and yield strength significantly, and the ductility of the alloy is similar to that without refiner addition. Additions of refiner improve the deformation formability of the AZ31 alloy.The extruded and hot rolled specimens (rods or sheets) with refiner addition are crack free and exhibit higher surface quality and mechanical properties than that without refiner addition.

Abstract: The thermodynamic analysis of the SiC/Al-Si-Mg system has been performed in order to find the conditions to produce SiC/Al-Si-Mg composite materials with the stable SiC/alloy interface (for both a-SiC and b-SiC) and with the solidification of primary a-Al solid solution. The conditions to avoid the formation of Al4C3 are expressed as function of temperature, and the silicon and magnesium content of the liquid aluminium alloy. It has been shown that to ensure stabilization of (the more stable) b-SiC, lower Si-content is needed and higher working temperature is allowed, compared to the requirements to stabilize (the less stable) a-SiC.