The Study Of Modification Of Late-model Al-Si Alloy Using For Cylinder Of Automobile Engine By Gravity Casting

Automobile industry is moving to the lightweight, high-speed, comfort, energy saving, low-emission direction, the heart of the engine as the car weighs about one-third of the weight of vehicle, its performance and weight is directly related to the value of the car. Use of aluminum engine not only can significantly improve engine performance, but also to reduce the weight of the engine. Domestic industrial production of aluminum cylinder block the slow development of three main subject areas: The cylinder body material performance cannot meet the requirements, the gravity casting industrialization technique of production is not mature, the production equipment is backward. The focus of future research is to solve the problem cylinder block material.Based on this, this topic further enhanced the new type of hypoeutectic Al-Si alloy overall performance through optimized compound modification processing. Using metal mold gravity casting, explored AlTi₅B, Al-10Sr and the compound rare earth single modification to this alloy organization and the performance influence; Optimizes the compound modification by the orthogonal testing method, and carries on the examination to the compound modified alloy's organization and the performance. Has used X-ray diffractometer(XRD), scanning electron microscope(SEM), the spectroscope and the optical microscope(OM) analyzes methods as well as the basic mechanical properties test method and so on to research it, and the results obtained are as follows:1,After AlTi₅B modification,the tensile strength and hardness of the alloy have increased significantly, while Ti=0.04wt.%, tensile strength and elongation and brinell hardness is reached its maximum, respectively 245.27 MPa, 2.535% and 80.24. RE modification significantly influences the elongation of this alloy, when RE=0.4wt.%,The minimum 3.03% also far higher than the 2.3% of master alloy. Sr modification, the tensile strength drops about 20Mpa and is quite small to the elongation and hardness.2,organization aspect: After AlTi₅B modification, Si becomes near spherical; due toα-phase attached on Al₃Ti, so that grain has been refined; bar shape AlCu changes from thickening to fine and plays a role in strengthening crystal boundary; The shape of impurity Fe becomes circle, weakened the negative influence. After RE modification, Si becomes short-stick; RE and Si, Cu have formed laminated T(AlSiCuNd), but in AlCu with Fe elements and so on has formed T(AlSiCuMnFeNiNd), the shape is more slender, has separated the aluminum base body seriously; The elongation remarkable enhancement is because in the 640℃rare earth phase rich Al and Al to form eutectic, these Eutectic structures form the skeleton in the crystal boundary place, plays the crystal boundary invigoration effect. The Sr modification is most ideal, but indicated to its bath surface oxide film analysis, SrO and Al₂O₃ form compound oxide compound SrAl₂O₄ causes the oxide film becomes looser, frail and extremely easy to crack, causes the smelting process inspiration to be serious, pinhole rate rise.3,orthogonal experiment results show that the optimization of complex modification treatment: Choosing the right value for tensile strength index W₁0.7, elongation index W₂0.2, hardness index W₃0.1 and comprehensive analysis of the results showed that: composite modifier of best-fit is Sr=0.01wt.%, RE=0.3wt.%, Ti=0.04wt.%.4,Test results of mechanical properties of the alloy after compound modification: tensile strength 232Mpa, elongation 2.66%, Brinell hardness 78.4, liquidity 22.1, a marked increase in overall performance to meet the preparation of car engine block requirements. Metallurgical structure analysis shows that: three kinds of modifier has been strengthened with each other.α-Al phase have been considerably refined and the grain outline clear, equiaxed grains account for large area; Si phase turns into the dot shape or granulated, modification effect is outstanding. Second, compared to Sr modification, pinhole was significantly reduced, and the grain boundary intermetallic compounds significantly reduced size, its shape into a feathery or like feathery.