Gravity casting automobile engine block with a new study of Al-Si Alloy Modification

Title: Gravity casting automobile engine block with a new study of Al-Si Alloy Modification
　　Author: Liu Guanglei
　　Degree-granting unit: Jiangsu University
　　Keywords: aluminum engine;; single degenerate;; compound modification;; microstructure;; mechanical properties
　　Summary:
　　Automotive industry is moving in the lightweight, high-speed, comfort, energy saving, low-emission direction, the engine as the heart of the car, weight about one-third the weight of the vehicle, its performance and weight is directly related to the value of the Strong magnets car. All-aluminum engine will not only significantly improve engine performance, but also reduce the weight of the engine. Domestic industrial production of aluminum cylinder block the slow development of three main subject areas: mainly the cylinder material properties, gravity casting mature industrial production process, production equipment behind. Focus of future research is to solve the problem of the cylinder material.
　　Based on this, this paper by optimizing the composite modification treatment to further improve the new hypoeutectic Al-Si alloy composite performance. Metal gravity die casting method, and explore the AlTi_5B, Al-lOSr and rare earth compound of single - and the deterioration of the properties of alloys; use of orthogonal test to optimize composite deterioration, and deterioration of alloy and composite performance testing. Using the X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy and spectroscopy analysis (OM) and other means as well as basic mechanical testing method was carried out research, the findings obtained are as follows:
　　1, AlTi_5B modification of the alloy tensile strength and hardness are improved significantly, when Ti = 0.04 wt.%, The tensile strength, elongation, and Brinell hardness reaches its maximum value, respectively 245.27MP_a, 2.535% and 80.24. RE elongation of the alloy deterioration have a significant effect, when RE = 0.4wt.%, The minimum 3.03% master alloy is also much higher than 2.3%. Sr deterioration, the decline in tensile strength of about 20MPa; of elongation and hardness are relatively small.
　　2, the organization: AlTi_5B degenerate into a nearly spherical Si phase after; as α-phase nucleation on the attached Al_3Ti, so that the grain has been refined; bar AlCu phase from coarse to fine and uniform distribution, serve to strengthen the grain boundary role; impurity Fe phase became round shape, weakened the negative impact. RE degenerate into Si phase after the short stick; RE and Si, Cu forming a sheet of T (AlSiCuNd) phase, and in the AlCu phase and with Fe and other elements to form a T (AlSiCuMnFeNiNd) phase, the shape is more slender, serious separates the Al matrix; elongation rate was significantly increased at 640 ℃ because of rare-earth phase and Al to form Al-rich eutectic, the eutectic grain boundary formation in the skeleton, played the role of grain boundary strengthening. Sr metamorphic most satisfactory, but their analysis showed that the melt surface of the oxide film, SrO and Al_2O_3 to form a composite oxide SrAl_2O_4 the oxide film becomes more porous, fragile and vulnerable to cracking, causing serious breathing smelting process, pinhole rate up.
　　3, the orthogonal experiment results show that the optimization of composite modification treatment: the right to choose a value of W1 tensile strength index of 0.7, elongation index has a weight of W_2 0.2, the hardness index of 0.1 weight is W_3 a comprehensive analysis of the results show that: the best compound modifier with the Sr = 0.01wt.%, RE = 0.3wt.%, Ti = 0.04wt.%.
　　4, optimization of complex modification of the mechanical properties of the alloy test results are: tensile strength 232Mpa, elongation rate of 2.66%, Brinell hardness, 78.4, 22.1 lattice mobility, overall performance has been significantly improved to http://www.chinamagnets.biz/Neodymium/Ball-Neodymium-Magnets.php meet the automotive engine cylinder preparation body requirements. IMF analysis showed that: three modifier role has been strengthened with each other. α-A1 phase greatly refined and clear outline of the grain, equiaxed total area; Si phase into dot-like or granular, metamorphic effect is excellent. Second, the deterioration of the alloy and Sr compared to the pinhole rate greatly reduced, and the grain boundaries of intermetallic compounds size is drastically reduced, and its shape becomes feathery or similar feathered.
　　Degree Year: 2010