Investigation on the effects of isothermal holding temperature and time on the coarsening mechanism and rheological properties of ADC12 Al semi-solid slurry

Abstract

The current work's key emphasis is on investigating the influence of isothermal holding temperature and time on the microstructural development and coarsening rate during the directly generated semi-solid slurry of ADC12 Al alloy from the cooling slope process. Additionally, a thorough investigation is conducted to optimize process variables in the rheo-pressure die-casting process to determine the correlation between the non-Newtonian flow behaviour and its morphological characteristics of the quenched slurry of ADC12 Al alloy. The obtained results inferred that with increasing isothermal holding time, average grain size marginally increases initially, then significantly increases with increasing time, while shape factor increases first and then declines. Furthermore, when isothermal temperatures increase, the average grain size rises, while the shape factor rises first before decreasing. As a result of the increase in grain size due to elevated processing temperature and prolonged processing time, the aluminium alloy's hardness deteriorated. The ideal condition for more spheroidization of α-Al in the synthesized semi-solid slurry of ADC12 aluminium alloys was at an isothermal temperature of 565 °C and a holding time of 7 min. Under ideal processing conditions, the alloy's grain size, shape factor, and hardness were 31 μm, 0.89, and 62.32 HV, respectively. The semi-solids of ADC12 Al alloy have a low coarsening coefficient. The coarsening rate constant at 565 °C was calculated using the Lifshitz-Slyozov-Wagner relationship, and a value of 37 μm3/s was discovered. The findings of the isothermal rheology experiment demonstrate that viscosity decreases as the shear rate increases, confirming the existence of shear-thinning actions in semi-solid slurries.