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

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A 356 is a hypoeutectic Al-Si alloy which has been widely used in many industrial fields owing to its good castability, low density, high corrosion resistance, and good weldability [1-3]. The T6 heat treated A356 has often been used in automobile wheel hubs [4-5]. In order to achieve good comprehensive performance, the most common method is adding less than 0.2wt.% of Ti to the Al-Si alloy to refine the grain size and obtain a fine-equiaxed structure. Al 3 Ti and α-Al have similar lattice constants, so the Al 3 Ti particles act as heterogeneous nucleation sites for α-Al grains and refine the microstructure of A356 [6,7]. However, a previous researcher found that the Al 3 Ti particles can only dissolve into liquid alloy at high temperature, which significantly deteriorates its refining effect [8,9]. As it was known, the mechanical properties of A356 are largely dependent on the size and morphology of eutectic Si phase. The T6 heat treatment can help

Diesel engines are used more and more widely in North America and Europe for passenger cars and light trucks because of their high fuel efficiency and reduced greenhouse gas emissions. These diesel engine components require a higher tensile property due to higher compression ratio and maximum breakout pressure of diesel engine compared with gasoline engines. Despite many advantages in the development of aluminum alloys, the alloys currently used for gasoline engine parts, typically A356 and 319 alloys, cannot meet the demand for high heat resistance [1][2][3][4][5] . In our previous work [6] , we studied the influence of the secondary dendrite arm spacing (SDAS) as well as the combination of the SDAS and the heat treatment parameters on the mechanical properties of a cylinder head of A356 alloy. We found that the A356 alloy cylinder head with smaller SDAS reached its peak value Abstract: Diesel engines, characterized by higher breakout pressure and compression ratio in comparison with gasoline engines, require particularly elevated tensile properties for their engine parts. In order to maintain both high strength and high ductility in the cylinder head, i.e., to obtain higher percent elongation without further reducing the tensile strength, AlSi9Cu1 alloy was used to prepare the cylinder head in an aluminum diesel engine. At the same time, the effect of different modification elements, Na or Sr, and Fe content on the reduction of secondary dendrite arm spacing (SDAS) was discussed, and the design of T7 heat treatment parameters were analyzed in order to improve the tensile ductility. The result shows: (1) The SDAS is as small as 18±3 µm for the Sr modified alloy. (2) The percent elongation of the alloy with Sr modification increases by 66.7% and 42.9%, respectively, compared with the unmodified alloy and the alloy with Na modification. (3) Lower Fe content alloy (0.10%) gives good results in percent elongation compared to the alloy with higher Fe content (0.27%); in particular, after Sr modification and T7 heat treatment, the elongation of over 5% is obtained. of hardness (HB), ultimate tensile strength (UTS) and yield strength (YS) at a lower aging temperature, but the over-aged structure was also yielded earlier. One of the most important factors that limit the use of A356 alloy for diesel cylinder head is its lower tensile properties at elevated temperatures: the properties of A356 (without Cu) alloy deteriorate seriously when temperature reaches 250 °C [1][2][3][4][5] . The diesel cylinder head being developed requires an optimum combination of strength and elongation: UTS ≥ 290 MPa, YS ≥ 240 MPa, percent elongation ≥4.5% and HB from 95 to 125, and for gravity casting, a value of SDAS not higher than 25 micron in the combustion chamber. To meet these requirements, we selected a candidate alloy containing copper -AlSi9Cu1 to produce the diesel cylinder head. The chemical compositions of the commercial AlSi9Cu1 are very similar to alloy 354 of the AFS (the American Foundrymen's Society). It is an alloy used by...

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