M. Chakraborty

Development of an efficient grain refiner for Al-7Si alloy and its modification with strontium

Abstract The grain refining response of Al and Al–7Si alloy has been studied with various Al–Ti, Al–B and Al–Ti–B master alloys at different addition levels. The results show that Al–B and B rich Al–Ti–B master alloys cannot grain refine Al, while they are efficient grain refiners to Al–7Si alloy. The level of grain refinement saturates after 0.03% of Ti or B for most of the master alloys studied both at short and long holding times. The grain refining efficiency of some elements other than Ti and B on Al–7Si alloy has also been studied. Interestingly, all the elements studied (B, Cr, Fe, Mg, Ni, Ti and Zr) have resulted in some grain refinement of Al–7Si alloy at short holding time and have shown fading/poisoning on long holding, which increased in the order of B (no poisoning), Ti, Cr, Ni, Fe, Mg, Zr. Sr (0.02%) has been found to provide complete modification of the eutectic in Al–7Si alloy within 2 min, which is not lost even after long holding up to 120 min. Significant improvements in the mechanical properties have been obtained by a combination of grain refinement and modification to an extent that was not possible by either of them alone.

Development of an efficient grain refiner for Al-7Si alloy

Abstract The response of Al–7Si alloy towards grain refinement by Al–Ti–B master alloys (with different Ti–B ratios) at different addition levels has been studied in detail. The results indicate that high B-containing master alloys are powerful grain refiners when compared to conventional grain refiners like Al–5Ti–lB master alloys. In the present study, indigenously developed master alloys have been used for the grain refinement of alloys Al–7Si and LM-25 . Significant improvements in mechanical properties have been obtained with a combination of grain refiner and Sr as modifier.

Effect of hot rolling and heat treatment of Al-5Ti-1B master alloy on the grain refining efficiency of aluminium

The influence of hot rolling and annealing of Al–5Ti–1B master alloy on its grain refining efficiency has been studied in detail. Both hot rolling and annealing improve the grain refining efficiency of the master alloy. Rolling results in the fracture of TiAl3 particles. The amount of deformation required for achieving good grain refinement decreases with increase in rolling temperature. Grain refining efficiency of the master alloy also increases with increase in annealing temperature. The improved grain refining efficiency of the master alloy on annealing is attributed to the increased fraction of TiAl3 and the possible formation of (Ti,Al)B2.

Effect of Thixoforming on the Microstructure and Tensile Properties of A356 Alloy and A356-5TiB2 In-situ Composite

In the present work, A356 alloy and in situ A356-5TiB2 composite feedstock was produced by employing Cooling slope casting technique. The technique resulted in near spherical morphology of primary α-Al phase in the feedstock of both the alloy and composite. A fine distribution of eutectic Si phase within the matrix was observed in the composite feedstock. The rheocast billets of both the alloy and composite were then thixoformed successfully at 50xa0% solid fraction temperatures of 580 and 585xa0°C respectively. Further, tensile properties of thixoformed alloy and composite were measured and compared with those of gravity-cast samples. It was observed that the % increase in yield strength and tensile strength of thixoformed alloy increased by 43 and 36xa0% respectively with respect to the gravity-cast alloy. The thixoformed composite attained the highest ultimate tensile strength of 211xa0MPa which is about 40xa0% higher as compared to gravity-cast alloy. Interestingly, the ductility of the composites is comparable to that of alloy after thixoforming.

Coarsening Kinetics of Semi-solid A356–5wt%TiB2 in situ Composite

An attempt has been made to investigate the coarsening behaviour of semisolid A356–5wt%TiB2 in situ composite produced by Cooling slope casting. It was found that the average grain size of α-Al in the gravity-cast alloy got reduced from 98 to 48xa0µm in the semi-solid A356–5TiB2 composite. The primary α-Al in the composite were found to undergo substantial spheroidisation after 5xa0min at a reheating temperature of 585xa0°C (fsxa0=xa00.5). Further, increase in holding time from 5 to 15xa0min resulted in grain growth of α-Al in both the alloy and the composites. The coarsening rate constant, K, for A356–5wt%TiB2 composite was found to be 339.73xa0μm3/s which is 32xa0% lower than that of semi-solid A356 alloy, thus proving the effectiveness of TiB2 particles towards grain coarsening.

Erosion Response of Thixoformed A356-5TiB2 in situ Composite Using Taguchi's Experimental Design

ABSTRACT The present article describes the application of Taguchis experimental design methodology to investigate the erosion wear behavior of in situ-formed A356-5TiB2 composite subjected to thixoforming. The effects of process parameters—such as impact velocity, erodent temperature, erodent size, standoff distance, and impingement angle—on the erosion rate have been analyzed. The results indicated that impact velocity is the most significant factor and accounts for 42.31% of the total effect on the erosion rate of the thixoformed A356-5TiB2 composite. It is found that material loss during erosive wear is primarily due to microploughing (i.e., abrasive type) and microfracture (i.e., impact type). The erosion rate of thixoformed A356-5TiB2 in situ composite was found to be 48.82 mg/kg, which is nearly 44% lower than that of as-cast alloy.

Optimization of process parameters during machining of thixoformed A356-5TiB 2 in-situ composite using Design of Experiments

The current work emphasizes Aluminum based metal matrix composites with TiB2 as reinforcement are emerging materials because of their potential for applications in automotive and aerospace industries. The machining of these materials has become a very important subject for research. This paper presents the application of Design of Experiments and analysis of variance in optimizing the machining process parameters such as cutting speed, feed rate and depth of cut, during turning operation. The response considered for the analysis was surface roughness. The results indicated that A356-5TiB2 composite produces higher tool wear, surface roughness and minimizes the cutting forces. Moreover, there was improvement in the quality of the machined surface in the A356-5TiB2 composite compared to A356 alloy. The chips formed during turning were characterized by Scanning Electron Microscope and analyzed from the machinability point of view. Optimum machining parameters for minimizing the surface roughness were determined. Thus, this work is an attempt to study the machinability behavior of thixoformed A356-5TiB2 in-situ composites.

Production of semi-solid feedstock of A356 alloy and A356-5TiB2 in-situ composite by cooling slope casting

Cooling Slope casting process has gained significant importance for manufacturing of semi-solid feedstock Al alloys and composites which find applications in automotive and aerospace industries. The primary objective of this research is to generate the semi-solid feedstock suitable for thixoforming process. The current work discusses the phenomena involved in the evolution of microstructure of the semi-solid feed stock by Cooling Slope casting process and the effect of various parameters. The process parameters like the angle and length of inclined plate affect the size and morphology of ?-Al phase. The Cooling slope process resulted in the formation of fine grain size of about 38 ?m of ?-Al phase, compared to that of 98 ?m processed conventionally. Further, the pouring temperature played a crucial role in the generation of semi-solid microstructures in case of both the alloy and composites. Moreover, fine TiB2 particles of size 0.2-0.5 ?m are uniformly distributed in the almost spherical ?-Al grains and at the grain boundaries in the composite feed stock. Cooling slope casting route is a suitable and economical route for semi-solid slurry generation by effectively varying the process parameters.