Abstract
The effect of the T6 heat treatment on the microstructure and hardness of a secondary semi-solid AlSi9Cu3(Fe) alloy have been investigated by using optical, scanning and transmission electron microscopy and hardness testing. The semi-solid alloy was produced using the swirled enthalpy equilibration device (SEED). The solution heat treatments were performed at 450, 470 and 490 °C for 1 to 6 h followed by water quenching and artificial ageing at 160, 180 and 220 °C for holding times ranging from 1 to 30 h. The microstructural investigations have revealed the spheroidization of the eutectic Si and the dissolution of the majority of Cu-rich compounds after all the solution heat treatments; moreover, the greater the solution temperature and time, the higher the hardness of the alloy. Unacceptable surface blistering has been observed for severe solution condition, 490 °C for 3 and 6 h. The artificial ageing at 160 °C for 24 h has led to the highest alloy strengthening thanks to the precipitation of β” and Q’ (or L) phases within the α-Al matrix. The hardening peaks at higher temperatures have been early achieved due to faster hardening kinetic; however, the lower number density of β” and Q’ (or L) phases and the presence of coarser θ’ precipitates result in a reduction of hardness values for peak aged condition at 180 and 220 °C, respectively.
Highlights
Aluminium-silicon casting alloys are widely used in the automotive industry due to their good castability, good corrosion resistance, high strength stiffness to weight ratio as well as recycling possibilities at low energy costs
Beside the use of vacuum-assisted high-pressure die-cast (HPDC) to reduce the level of entrapped gas [4], semi-solid metal (SSM) processes have been considered a valid alternative for producing sound Al-Si-based light-weight parts with satisfactory response to heat treatments, especially for the automotive sector
Automotive components were manufactured with a secondary AlSi9 Cu3 (Fe) alloy (EN AC-46000) by the Swirled Enthalpy Equilibration Device (SEED), which operates by using a liquid-based method for producing the Al slurry over a wide range of Al-Si alloy compositions [18,19]
Summary
Aluminium-silicon casting alloys are widely used in the automotive industry due to their good castability, good corrosion resistance, high strength stiffness to weight ratio as well as recycling possibilities at low energy costs. The application of a post-casting thermal treatment on high-pressure die-cast (HPDC) components is still a limited practice in industry. Due to the extreme turbulent flow of molten metal during filling of the die cavity, internal or sub-surface porosity, originated from entrapped gases, can usually occur in the diecastings [1]; during typical thermal treatment at elevated temperature (470÷500 ◦ C [2]), gas expansion can produce unacceptable surface blisters on the components [2,3]. Beside the use of vacuum-assisted HPDC to reduce the level of entrapped gas [4], semi-solid metal (SSM) processes have been considered a valid alternative for producing sound Al-Si-based light-weight parts with satisfactory response to heat treatments, especially for the automotive sector. Some examples are fuel rails, control arms, steering knuckles, engine brackets, or even engine blocks [5,6,7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
