Improve mechanical properties of high pressure die cast Al9Si3Cu alloy via dislocation enhanced precipitation

Abstract

To improve the properties of high pressure die cast Al9Si3Cu alloy, melt treatment via high shear was employed to form fine in-situ MgAl2O4 particles which act as potential nuclei to refine α-Al grains whilst providing reinforcement to enhance the tensile strengths of the alloy. Experimental results showed that the naturally formed MgAl2O4 particles in the alloy melt were approximately 1 µm in diameter and are very limited in number as observed in the concentrated samples obtained via filtration. With the implementation of the high shear technology on the alloy melt, it is possible to synthesize a large number of fine MgAl2O4 particles which were approximately 80 nm to 300 nm in diameter. The yield strength of the alloy containing such in-situ sub-nano-sized particles was found to increase from 147 MPa to 169 MPa in the as-cast state. Following treatment with direct ageing at 155°C only, the yield strength of the alloy treated with high melt shear was found to increase by 128 MPa, ultimately achieving a yield strength and ultimate tensile strength of 297 MPa and 423 MPa respectively. The improvement of the mechanical properties of the alloy is attributed to the fine and uniform microstructure achieved by the enhanced heterogeneous nucleation of both α-Al grains and α-AlFeMnSi intermetallic compound via the in-situ MgAl2O4 particles, and also to the enhanced precipitation strengthening trigged by the increased dislocation density caused by the in-situ MgAl2O4 particles.

Microstructure and mechanical properties of new die-cast quaternary Al-Cu-Si-Mg alloys

“…Although these die-cast alloys have yield strengths close to or over 200 MPa, the elongation to failure is relatively small (e.g. below 3%), resulting from increased volume fraction of copper-/zinc-contained intermetallic compounds [2,36,40,41].…”

Influence of porosity characteristics on the variability in mechanical properties of high pressure die casting (HPDC) AlSi7MgMn alloys

“…The precipitate was identified to be β'' with a monoclinic structure and the orientation relationship is <230> Al //<100> β'' , <-310> Al //<001> β'' A proper ageing treatment after the solution process can promote the formation of the precipitates according to the chemical composition, resulting in the enhancement of strength. This is another important strengthening mechanism for Al alloys called precipitation strengthening [10,56,57]. For Al-Si-Mg based alloys, the possible precipitates are β'' (Mg 5 Si 6 ), β' (Mg 9 Si 5 ) and β (Mg 2 Si) phase [58][59][60].…”

“…2-4 m• s -1 to complete the filling of the die cavity. The third movement occurs during the intensification stage, which aims to feed solidification shrinkage by the movement of the last solidifying melt under a high intensification pressure typically between 20-100MPa [9][10][11]. Additionally, during intensification the majority of air entrapment resulting from fluid flow in the shot sleeve is compressed to a considerable small size under the applied pressure.…”

Understanding of surface segregation of Cu and Zn on nano Si precipitates to the mechanical property improvement of high pressure die casting Al9Si3CuFe alloy

“…In our previous study [21], the elongation of HPDC A380 alloy increased from 4.9% to 5.4% following the addition of in-situ Mg 2 AlO 4 particles as grain refiner-the variability in elongation and yield strength was also reduced. With direct aging treatment for HPDC LM24 alloy containing in-situ MgAl 2 O 4 particles [22], a significant improvement of tensile strength is achieved whilst maintaining the elongation of the base alloy. However, the precipitation strengthening mechanism in LM24 alloy having in-situ MgAl 2 O 4 particles is not fully understood.…”