| A kind of original discontinuous function gradient composites (FGM) used in substituting the conventional thin wall cast iron cylinder liner was proposed and trial-produced by the centrifugal casting process. There are two layers in the radial wall of the tubes. The reinforcement layer in the inner layer with the large number of in-situ reinforcement particles, and that has the high hardness, the fine wear-resisting performance, the good heat conduction performance as well as the thermostability. The un-reinforcement layer in the outer layer without the particles or a little of particles, that has the high tensile-strengthen as well as the good machine-finishing performance. The structure and properties present the discontinuous gradient distribution and change from the inner to outer layer. In order to get the target, electing in-situ particles, designing material composition, establishing centrifugal casting parameter, fabricating rough shell, testing properties were systematically investigating, respectively.The structure and properties of only the primary Si and the primary Si, Mg2Si jointly reinforced Al based gradient function composites show that, the only primary Si particles reinforced continuous gradient function composites can be fabricated by hot mould centrifugal casting, but the primary Si and Mg2Si particles jointly reinforced discontinuous gradient function composites can be obtained by the same process. The stress and movement velocity of the particles in the centrifugal field shows that the primary Mg2Si particles have the higher centripetal moving velocity than the primary Si particles. During centripetal moving, the Mg2Si particles would impact and then drive the primary Si moving together towards to the inner layer, and form the discontinuous gradient function composites. Wearing properityies of two kinds of composites show that the primary Si is the main facter to increase the wear-resistance of composites, and the primary Mg2Si is the secondary reinforcement particles to exploit enough the wear-resistance of the primary Si particles.Studying on the material composition shows that the pattern of the Mg2Si is the alternative key factor forming the discontinuous gradient function composites by centrifugal casting. Only the massive primary Mg2Si has the higher centripetal velocity and may drive the primary Si to move together towards to the inner layer. The nodular and network eutectic Mg2Si does not shift or has very fine centripetal velocity. So only the Al-Si-Mg alloys that can form a lagge number of massive primary Mg2Si may fabricate the primary Si and Mg2Si jointly reinforced Al based discontinuous gradient function composites by centrifugal casting. And the reasonable alloying composition that satisfying the mention above is Mg≥4wt% and Si≥19wt%.The primary Si and Mg2Si segregating aggregation in the inner layer increases the processing difficulty and results the shrinkage cavity and blow hole forming in the face of the inner and outer layer in the process of centrifugal casting. Forming mechanics of shrinkage cavity shows that a freezing character of solid—liquid—semi-solid—solid was formed from the ectotheca to the inwall of tubes in centrifugal casting. So the liquid between the two layers freezes in the time of freezing terminal, and it results to the shrinkage cavity forming in the interface of the two layers. The blow hole forming process shows that, the supersaturation gas in the Al fused mass was separated out under the 660℃that a number of primary particles have already aggregated in the inner layer.So the gas with the smaller density is trapped in the interface and inner layer during outflowing from the inwall.The appropriate processing parameters are that: point of pouring is 660~670℃, the preheating temperature of the mold is 200~300℃, the spraying time is 60s, pouring procedure is controlled in the low velocity (100~150r/min), side pouring in the outer port. When these processing parameters are adopted the blow hole is reduced or vanish, and the shrinkage cavity is reduce and controlled in the outer port of the tubes that does not effect the residual tubes after the shrinkage cavity is removed by turning.The cylinder liner semifinished materials were produced according to some model water cooling thin wall cylinder liner components size, and then some of them was carried on the T6 heat treatment and turning. The turning processing proof that, the inner layer of the tubes is hard and owns the fine wear-resisting properties, and the outer layer has the good turning workability.The organization evolving characteristics of the different heat treatment condition demonstrate that, as casting, the primary Si and Mg2Si particles is tiny, and the size of the former is under 60μm,the latter is under 25μm .Both of them present the irregular multilateral shape, and has the union gap with the substrate between. The eutectic Si is tiny bangding, and the eutectic Mg2Si is clustering and network. After heat-treating, the primary Si and Mg2Si were dissolved in the edge angle and formed the rounded particles, and the gap between the particles and matrix vanishes. To the eutectic Si and Mg2Si during solution heat-treating, the former was dissolved and formed the short stick, and the latter was dissolved mainly and formed the tiny tubercles dispersing distribution among the Al matrix. And after aging heat-treating, the un-dissolved eutectic Si and Mg2Si grow up again that the size is over 5μm.The mechanical properties show that, the hardness, specific elongation and tensile-strength of the solution heat-treated condition are the best, and reach individual HRB70 (un-reinforcement layer) and HRB90 (reinforcement layer), 1.15% and 210MPa. But to wear-resisting property, the reinforcement layer of the artificial aging blank is the best and the wearing capacity is only 0.009g. The growed-up eutectic phase after artificial aging together with the two primary particles form the four grades reinforcement particles, and reinforcement model is similar to"sand-stone"of the concrete. The model is good at increasing the wear-resisting properties, but decreases the tensile-strength. The linear expansion factor of the artificial aging blank is 18.9×10-6/℃(20～100℃),19.61×10-6/℃(20～200℃) and 20.48×10-6/℃(20～300℃), and those are better than ZL109 alloys.The results of contrasting with the some cast iron cylinder liner show that the mechanical and thermophysics properties of the composites have already approached or reached application-required properties. So the composites own the possibility as the substituting materials of the conventional cast iron cylinder liner.
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