Characterization and kinetic modeling of secondary phases in squeeze cast Al alloy A380 by DSC thermal analysis

Abstract

A l-Si-Cu alloys are increasingly used in various automotive applications in the consideration of less weight and less energy consumption versus ironbased alloys. Among the Al-Si-Cu casting alloys, A380 with a silicon content of 7.5-10wt.% is the most widely used one due to its excellent castability, moderately high strengths and low cost [1] . To produce A380-based components, high pressure die casting (HPDC) is usually employed as a primary manufacturing process because of its high production rate and dimensional accuracy and stability. Most components produced by HPDC have relatively thin cross sections with a predominant wall thickness of 5 mm. High-pressure die castings have relatively high gas porosity levels, particularly in an area Abstract: Thermal analyses on squeeze cast aluminum alloy A380 (SC A380) solidified under 90 MPa were carried out to study the microstructure development of the alloy, in which a differential scanning calorimeter (DSC) was employed. During the DSC runs, heating and cooling rates of 1, 3, 10, and 20 °C•min -1 were applied to investigate the heating and cooling effects on dissolution of secondary eutectic phases and microstructure evolution. Various reactions corresponding to troughs and peaks of the DSC curves were identified as corresponding to phase transformations taking place during dissolution or precipitation suggested by the principles of thermodynamics and kinetics. The comparison of the identified characteristic temperatures in the measured heating and cooling curves are generally in good agreement with the computed equilibrium temperatures. The microstructure analyses by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) indicate that the distribution and morphology of secondary phases present in the microstructure of the annealed sample are similar to the as-cast A380, i.e., strip β(Si), buck bone like or dot distributed θ(Al 2 Cu), β(Al 5 FeSi) and with relatively thick cross sections, owing primarily to the entrapment of air or gas in the melt during the high-speed injection of turbulent molten metal into the cavity. A recent study indicates that squeeze casting (SC), involving slow laminar filling and the solidification of a molten metal in a closed die under an applied pressure, is capable of eliminating gas and shrinkage porosity and consequently enhancing the tensile properties of A380 castings with very thick sections (25 mm) over the HPDC counterpart [2] . The improved soundness of squeeze cast A380 casting enables thermal treatment for further improvement of mechanical properties. Thus, an in-depth understanding of the kinetic features of the dissolution and precipitation of secondary intermetallic phases in squeeze cast A380 alloy is needed to establish correct thermal treatment processes and comprehend their effect on microstructure evolution.It has been demonstrated in previous studies [3] that the mechanical properties of cast A380 are related to the presence of secondary intermetallic phases and their

Effect Mechanism of Sc Addition and T6 Heat Treatment on Precipitated Phase and Mechanical Properties of Al‐Cu‐Mn Alloy

“…When the concentration of the two kinds of atoms reaches the eutectic composition, α‐Al + θ (Al 2 Cu) binary eutectic or α‐Al + θ (Al 2 Cu) + T(Al 12 CuMn 2 ) ternary eutectic will be formed in the alloy. [ 25 ] Usually, the as‐cast structure of the alloy is α‐Al + θ (Al 2 Cu) binary eutectic is dominant, with a small amount of T(Al 12 CuMn 2 ). When the diameter of the dispersed precipitate particles in the alloy exceeds a certain critical value, the coherent relationship with the matrix will be lost, the lattice mismatch will occur between the dispersed precipitate particles and the matrix.…”

The Role of Mg Content and Aging Treatment on the Tensile and Fatigue Properties of Die-Cast 380 Alloy

“…The results show that by increasing the V concentration from 0% to 1.05%, the average length and volume fraction of the β-Al 5 FeSi phase is reduced to 30 µm and 1.44%, respectively. When the melt is solidified under high pressure, the solute diffusion coefficient is decreased, whereas the liquidus temperature and solid solubility of the solute element are both increased [22][23][24][25]. This process leads to the precipitation of different phases coupled with marked grain refining which may be attributed to the precipitation of fine Si 2 V phase particles.…”

Comparative Study of the Metallurgical Quality of Primary and Secondary AlSi10MnMg Aluminium Alloys

“…The ductility obtained from parts cast by V-HPDC is significantly higher than that of conventional HPDC technology. Considering the UNE-EN-1706:2020 standard as a reference, the minimum elongation required for the AlSi9Cu3(Fe)(Zn) alloy (the most used secondary alloy in conventional HPDC process [6][7][8]) is 1% in the F state, whereas for a V-HPDC component cast in AlSi10MnMg, a minimum elongation of 12% is required after T7 heat treatment [3][4][5][6][7]. This huge difference in elongation is associated with the different compositions and microstructures of both alloys, with the higher melt cleanliness [9,10] and the lower porosity being achieved using vacuum application in V-HPDC.…”