Spheroidization and Coarsening of Eutectic Si Particles in Al-Si-Based Alloys

The present study was carried out on three Al-Si cast alloys viz., 319, 356, and 413 alloys, solidified at 8°C/s. Samples from 319 and 413 alloys were solution heat-treated at 510°C, whereas samples from 356 alloy were solutionized at 550°C, for up to 1200 h. The results reveal that complete spheroidization of eutectic Si particles in terms of achieving individual spherical particles cannot be achieved in most Al-Si-Cu-Mg alloys even after a solutionizing time of 1200 h which contradicts with the existing theory. Addition of Sr to Cu-free 356 alloy could lead to complete spheroidization after 1200 h at 550°C if the alloy was solidified at 8°C/s. Besides the dissolution theory of Ostwald, coarsening of Si particles can as well take place by impingement, fusion, and agglomeration. Increasing the Si content makes it difficult to achieve spheroidization, i.e., fragmentation and coarsening. Results obtained from observations of deeply etched samples (3D) contradict those obtained from polished samples (2D).

Process Optimization on Hardness of Precipitation Hardened Al6061 Alloy Using Design of Experiments

Aluminium is ranked after iron and steel in the metal market. Aluminium 6061 alloy has been selected by many designers and engineers for different kind of applications. Further, its strength can be improved by cold working, refinement of grains, precipitation and dispersion hardening. In this work, trials are conducted for the investigation of the effects due to age hardening parameters like, solutionizing time, temperature and time for aging on hardness of 6061 Aluminium alloy using Design of Experiments. The response is predicted by using linier regression model. From the results it can be perceived that, the ageing temperature and aging time have a substantial effect on the response whereas, solutionizing time does not have a significant effect. For a specific set of parameters the hardness is improved from 50 to 74 BHN, resulted in an increase in hardness by about 50%.

Fluidized bed heat treatment of aluminum cast components

Heat Treatment and post casting treatments of cast components has always been an important step in the control of microstructure, and resultant properties. In the past, the solutionizing, quenching and ageing process steps may have “required” in total over 20 hours of processing time. With the advent of fluidized bed reactors (FB), processing time has been dramatically reduced. For example, instead of 8-10 hours solutionizing time in a conventional furnace, the time required in FB is less than an hour. Experiments with Al-Si-Mg alloy, (both modified with Sr, and unmodified) were performed, having different diffusion distances (different DAS), and for different reaction times and temperatures. Both the model and the experimental results are presented and discussed.