Study On Mechanical Properties Of Alloy ZL108 Made From Electrolytic Low Titanium Aluminum Alloy

Alloy ZL108 is a main brand of cast aluminum alloy used for power engine piston material, it is not needed to contain titanium according to the national standard now. It is believed popularly that adding small amounts of titanium could refine the grains and improve the mechanical properties of aluminum alloy. Therefore, it is the subject of this paper to see if it can improve the mechanical properties of alloy ZL108 either.Electrolytic low titanium aluminum master alloy is a new developed aluminum alloy. It is developed by Zhengzhou University and electrolytic aluminum factory corporately. Compared with the traditional technology of adding titanium by melting, it has the advantage of low cost, simple technology, high efficiency of reclamation and easy control of contents. It does not need to change the original technology or add more equipment to make alloy ZL108 containing titanium, and this technology is called electrolytic adding titanium.Because of the hard running condition of piston in power engine, it is demanded that its material should possess enough resistance abilities against high temperature, fractional wear, possess excellent dimensional stability and so on. It is the main subject of this paper to study the influence of electrolytic adding titanium on the properties of tensile underroom and high temperature, fatigue and fracture toughness, and fractional wear of alloy ZL108. This is the necessary fundamental research for applying the electrolytic low titanium aluminum master alloy to alloy ZL108 at the first stage. Of course, the subject is of real significance.In this paper, the alloy ZL108 containing 0.2% titanium is made from electrolytic low titanium aluminum master alloy, named as alloy ZL108Ti. Two groups of specimens are made by melting and casting, one contains no titanium and the other contains titanium, both of them were undergone the same technology of melting, heat treatment and machining. After comparative mechanical tests, the test results were analyzed with the statistics method, and the data were undergone the significance tests of F distribution, t distribution and t'distribution. At the significance level of 5%, it has been found that the tensile strength and hardness of alloy ZL108 at room temperature and high temperature are raised by electrolytic adding titanium, the plane strain fracture toughness is also raised, and the resistance against fractional wear is improved obviously.In the view of the microstructure analysis, it is the function of refining grains of alloy ZL108 by electrolytic adding titanium that raise and improve the mechanical properties of alloy ZL108. After electrolytic adding titanium, the first dendrite of alloy ZL108 gets smaller obviously, the second phase components are distributed more evenly, and the separation between the second dendrite arms gets smaller andhomogeneous, the shape of silicon particle is more homogeneous and near spherical.There are two mechanisms of refining the grains of alloy ZL108 by electrolytic adding titanium. On one hand, titanium exists in the melt of aluminum alloy in the diffusive form of a plenty of small Al3Ti particles, and the high contents of silicon particles substitute the compound Ti (Ali^Si^ for TiAl3, both of them have the heterogenous nucleate ability, which increase the a(Al) phase nucleate rate. On the other hand, the component super cooling of titanium element makes a(Al) phase nucleate more easily.