Role of Temperature and SiCP Parameters in Stability and Quality of Al-Si-Mg/SiC Foams

Composites of Al-Si-Mg (A356) alloy with silicon carbide particles were synthesized in-house and foamed by melt processing using titanium hydride as foaming agent. The effects of the SiCP size and content, and foaming temperature on the stability and quality of the foam were explored. It was observed that the foam stability depended on the foaming temperature alone but not on the particle size or volume percent within the studied ranges. Specifically, foam stability was poor at 670A degrees C. Among the stable foams obtained at 640A degrees C, cell soundness (absence of/low defects, and collapse) was seen to vary depending on the particle size and content; For example, for finer size, lower particle contents were sufficient to obtain sound cell structure. It is possible to determine a foaming process window based on material and process parameters for good expansion, foam stability, and cell structure

Effect of matrix strength on the mechanical properties of Al-Zn-Mg/SiCp composites

The mechanical properties of Al-Zn-Mg alloy reinforced with SiCP composites prepared by solidification route were studied by altering the matrix strength with different heat treatments. With respect to the control alloy, the composites have shown similar ageing behaviour in terms of microhardness data at 135 degrees C. It was shown that although composites exhibited enhanced modulus values, the strengthening was found to be dependent on the damage that is occurring during straining. Thus the initial matrix strength plays an important role in determining the strengthening. Consequently, compression data had shown a different trend compared to tension. (C) 2000 Elsevier Science Ltd. All rights reserved

Microstructural evolution in liquid metal processed Al-alloy/SiCp composites

Al-Zn-Mg/SiCP composites processed by a liquid metal processing (stir casting) technique have been microstructurally characterised in the as-cast and extruded conditions. Uniform distribution of SiCP is observed with few defects, such as particle clusters, which are due to partial wetting and associated gas porosity. The constituent particles are associated with SiCP although their composition remains unaffected compared with the control alloy. Hot extrusion of the composite using a shear type die showed banding of particles in the extruded direction with 9 vol.% composite. Such defects however, are not predominant in 18% SiCP extruded composites. The presence Of Mg2Si is detected at the particle matrix interface as well as in the matrix

In-situ phase transformation studies of Ni48Mn39In13 melt-spun ribbons

The phase transformation in Ni48Mn39In13 melt-spun ribbons has been studied by employing in-situ transmission electron microscopy (TEM) techniques. At room temperature, the investigations showed the martensite phase consisting of plates with internal stacking faults. This phase exhibited the presence of 7M and 5M modulations. In addition, a small volume fraction of the austenite phase was observed. Upon in-situ heating from room temperature to 95 degrees C, the martensite phase transformed to austenite phase. However, in the subsequent cooling-heating cycles, the martensite phase was retained at high temperature. We discuss our experimental observations and the possible mechanisms for the stabilization of the martensite phase due to thermal cycling. (c) 2012 Elsevier Ltd. All rights reserved

Structure, magneto-structural transitions and magnetocaloric properties in Ni50-xMn37+xIn13 melt spun ribbons

Melt spun Ni50-xMn37+xIn13 (2 <= x <= 5) ribbons were investigated for the structure, microstructure, magneto-structural transitions and inverse magnetocaloric effect (IMCE) associated with the first-order martensitic phase transition. The influence of excess Mn in Ni site (or Ni/Mn content) on the martensite transition and the associated magnetic and magnetocaloric properties are discussed. It was found that with the increase in Mn content, the martensitic transition shifted from 325 to 240 K as x is varied from 2 to 4, and the austenite phase was stabilized at room temperature. The x=5 ribbon did not show the martensitic transition. For the x=3 ribbon, the structural and magnetic transitions are close together unlike in the x=4 ribbon in which they are far (similar to 60 K) apart. The zero field cooled and field cooled curves support the presence of exchange bias blocking temperature due to antiferromagnetic interactions in the ribbons. A large change in the magnetization between the martensite and austenite phases was observed for a small variation in the Ni/Mn content, which resulted in large IMCE. A large positive magnetic entropy change (Delta S-M) of 32 J/kg K at room temperature (similar to 300 K) for a field change of 5 T with a net refrigeration capacity of 64 J/kg was obtained in the Ni47Mn40In13 ribbon. (C) 2011 Elsevier B.V. All rights reserved