Fabrication Of Aluminum Based Composites Cylinder Liner Reinforced With In Situ Particles And Its Application

The centrifugal casting process was adopted to fabricate a new lightweightaluminum matrix composite material cylinder liner reinforced with in-situ particulate,and the system experimental studies were carried out to realize the application of thealuminum alloy cylinder liner in the engine.The centrifugal casting process was used to prepare Al-18Si-7Mg, Al-18Si-7Ni andAl-18Si-7Ti composite materials which contain different in-situ particles. The X raydiffraction, scanning electron microscopy, X ray energy spectrometer and opticalmicroscopy were adopted to analyze the microstructures of the composite materials, andthe mechanical properties of them were tested as well.It is found that a large number of primary Si/Mg₂Si particles were segregated in theinner layer of Al-18Si-7Mg casting, while no particle was in the outer layer. Themaximum particle volume fraction in the inner layer was up to24.16vol.%, whichcontributed the highest hardness and superior wear resistance for the casting. Thus,among the three alloys, Al-18Si-7Mg was most suitable for use in the preparation ofaluminum alloy cylinder sleeve. In order to make the Al-Si-Mg alloy cylinder liner beapplied in the engine, the preliminary researches of material composition, centrifugalcasting parameters, the metaphase study of the quality control of the fabrication ofcylinder liner blanks and the later stage experiments of the die-casting technology, themachining process, the inner surface processing of the cylinder bore and the bench testof the cylinder liner were implemented. A self-made device was used to measure theheat transfer performance of the aluminum alloy cylinder. A Road test was conducted toexamine the use of the all-aluminum engine assembled Al-Si-Mg alloy cylinder sleeve.Through material composition research, it is found that in the Al-xSi-yMg alloy,primary Si and Mg₂Si are formed on the condition of x≥12.8＋0.49y, y≥5（15≤x≤30,y≤8）; only primary Si particles are formed on the condition of x≥12.8＋0.49y, y<5; onlyprimary Mg₂Si particles are formed on the condition of x<12.8＋0.49y, y≥5; and noparticle is formed on the condition of x<12.8＋0.49y, y<5. With the increase of Sicontent （constant Mg content）, the ratio, k, describing the particle accumulation area interms of the whole cross section of the casting, increased gradually. With the increase ofMg content （constant Si content）, a different variant rule of k occurred: as m（Si）≤20%, kdecreases first and then increases with the increase of Mg content; as m（Si）≥25%, k increases continuously with the increase of Mg content.Through the studies of forming process to the castings, it is found that the value ofk increased gradually to the peak of0.59with the ascendant pouring temperature andmold temperatures; the value of k gradually decreased from1.0to0.53with the increaseof centrifugal speed. With the changed processing parameters, the volume fraction andthe size of primary Si, Mg₂Si particles show different gradient distribution. Themorphologies of particles also produce bigger change, their roundness values, F,appearing a very low value of0.3～0.5.According to the different dimensions of cylinder liners, the air-cooled engine of149cc and109cc cylinder blank from Zongshen, and the water-cooled engine of600cccylinder blank from Jialing and1300cc cylinder blank from DFSK were fabricated bycentrifugal casting. It is found that the holes and cracks in castings can be eliminatedthrough reducing the pouring temperature. The slag inclusions and impurities can bereduced by using homemade argon "static blowing" device to purify the melt, and theslag can be collected by improving the centrifugal speed. Thus, the quality control ofcylinder blanks is realized through machining.A suitable mold size and casting size are necessary conditions to obtain cylinderliner products having ideal thickness of particle segregation layer. Taking the cylindersize of149cc engine from Zongshen as an example, set the wall thickness of a castingxmm, then, the original minimum thickness of segregation layer in the casting is0.45xmm, the machining dimension of the inner surface is b≥3.0mm, and the remainingthickness value of the segregation layer is d≥1.5mm. Set the inside diameter of the moldis ymm, and the rough machining size of inside diameter of the cylinder liner is knownof62mm. As a result, the inside diameter of the mold should be79.3mm, the wallthickness of the casting ranges from11.65mm to13.0mm, the thickness value of thesegregation layer is5.24≤f≤5.85mm, the cutting value of the inner surface is3.0≤b≤4.35mm, the remaining thickness of the segregation layer is1.5≤d≤2.24mm, and the theory turning value of the outer surface of the castingcasting is c=2.15mm.During the process of high pressure die casting, the larger thermal expansion ofaluminum alloy cylinder liner would cause the action of "running water" in the cylinderbody, therefore, the machining dimension of the cylinder bore needs a appropriatereduction. Generally speaking, a lower value in the processing scope is accepted.During the process of low pressure die casting, the cavity tends to be incomplete filled as a result of a low preheated temperature of the aluminum cylinder liner, therefore, theworking pressure of the die casting machine should be appropriate to increase.Through the theory calculation of heat transfer of aluminum alloy cylinder sleeve–aluminum block and the cast iron cylinder liner-aluminum cylinder block, it is foundthat the heat transfer ability of aluminum alloy cylinder sleeve is more than twice thanthat of cast iron cylinder liner. Through the “experiment of temperaturemeasurement-data of curve fitting” method, it is the first time to find that thetemperature of the inner surface of the aluminum block is231°C while it is242°C forthe iron cylinder liner-aluminum cylinder block, which proves that aluminum alloycylinder has a better heat transfer performance.The traditional honing processing was adopted to machine the inner surface ofaluminum alloy cylinder sleeve, and it is found that the formed cross reticulate is toorough, so that the phenomenon of piston scraping is easy to occur in the bench test.Through experimental exploration, the combination of honing process and a homemadeSiC-felt polishing device is proved to be feasible to produce appropriate reticulates inthe inner surface of aluminum alloy cylinder sleeve.Using10wt%NaOH solution to corrode the aluminum alloy cylinder liner used in109cc air-cooled engine from Zongshen at25°C, it is found that the measurement oftotal （HC+NOx） emissions rose by10%than that of cast iron cylinder liner during thebench test, which is not beneficial to exhaust emissions. After the corrosion treatmenton aluminum alloy cylinder liner used in600cc water-cooled engine from Jialing, themeasured maximum engine power and engine torque reach22.66kw and44.37N·m,respectively, in the bench test, which meets the original design demand. Also, thetemperature of the aluminum cylinder is significantly reduced during bench test.A road test was carried out on corroded aluminum alloy cylinder liner used in1300cc water-cooled engine from DFSK. The aluminum alloy cylinder liner assembledin an engine has now completed an initial test phase of30000km, and runs well atpresent, which is expected to be applied.