Study On The Process Of Magnesium Alloy Crankcase Right Cover Of Motorcycle

Magnesium alloy with some good properties such as high specific strength, damping vibration, casting technic and so on, is the lightest material of commercial structure materials in industrial applications and one of the most promising lightweight materials currently. Motorcycle as an inexpensive and convenient transportation, its lightweight and energy saving and emission reduction is an important direction of technical progress. Crankcase is an important part of motorcycle transmission system, generally formed by aluminum alloy die casting. The replacement of magnesium alloy can not only lose weight about one-third, but also make use of excellent damping vibration reduction performance of magnesium alloy to reduce vibration and noise, thus improve the comfort of motorcycle.Combined with the engineering requirement of crankcase development of magnesium of an enterprise, the die cast process of crankcase right cover of AZ91-1.5Si-0.4Ca magnesium alloy was studied. There were two aspects had been emphatically analyzed: First, the different thickness of slabs casting samples were designed, in addition, simulation was taken to get the solidification rate of different thickness of slabs casting samples, and the microstructure, ambient temperature and 180? mechanical properties, and tensile fracture morphology were studied by XRF, XRD, OM, SEM/EDS, and universal testing machine to provide theoretical basis on microstructure and mechanical properties of die cast AZ91-1.5Si-0.4Ca by controlling the wall thickness and solidification rate. Second, the crankcase right cover structure was analyzed, and the orthogonal experiment and simulation were designed according to actual production and the above research results, the die casting process of crankcase right cover was designed and optimized, and samples were produced to verify the optimized process parameters.The main research results and conclusions are as follows:(1) In AZ91-1.5Si-0.4Ca die-casting alloy, Si mainly exists in the form of Mg2 Si which has two forms of eutectic first primary Mg2 Si and eutectic Mg2 Si, and Ca mainly exists in the form of solid solution.(2) With wall thickness of die-casting samples decrease, the solidification rate increases, the two alloys show a certain trend of grain refinement, and Mg2 Si in AZ91-1.5Si-0.5Ca change from bulky polygon and Chinese script type to fine polygon and short rod.(3) The tensile strength of AZ91-1.5Si-0.4Ca at 180 oC is higher than that of AZ91 when the section thickness is less than 2.5mm, and the tensile strength of AZ91-1.5Si-0.4Ca at ambient temperature is higher than that of AZ91 when the section thickness is less than 3mm.(4) The mechanical properties of AZ91-1.5Si-0.4Ca and AZ91 at ambient temperature and 180 oC increase with the increase of solidification rate, i.e. the decrease of section thickness. The influence of section thickness on tensile strength of AZ91-1.5Si-0.5Ca is greater than that of AZ91, but the influence on elongation is less than that of AZ91. Furthermore, in the condition of same solidification rate, the elongation at ambient temperature and 180? of AZ91-1.5Si-0.4Ca are lower than that of AZ91, and the fracture form is more tend to brittle fracture.(5) The solidification rate is greater than or equal to 29.2741 can ensure Mg2 Si distribute in the form of fine polygon and short rod, which can improve the mechanical properties at ambient temperature and 180?.(6) The results of simulation on crankcase right cover show that the faster the slow injection speed is, the shorter the liquid metal filling time is, the less stable the liquid metal is, and the bigger the maximum rate of solidification is; and the higher the mold temperature is, the longer the time of solidification will be; and the faster the slow injection speed is, the higher the solidification rate will be. While the influence of the above four factors on die casting defects are similar, and the defects exists in the thick wall near the thin-walled shell.(7) It's hard to obtain the ideal solidification rate by regulating the die casting parameters, while adding water cooling pipe on crankcase right cover can improve the solidification rate of threaded hole and the surrounding shell, which can modify the microstructure and improve the quality of production.