Research On The Effects Of Modified Metal Additives On The Microstructure And Properties Of Cast Zinc-aluminum Alloy

Due to the good casting performance, good cost performance and many other advantages, Zinc-aluminum alloy has been widely used in various fields. But its application has been widely limited as its limited plasticity, toughness, easy to aging and other shortcomings. As the high melting point, high hardness and good compatibility with liquid metal and many other attributes, modified superfine SiC powders have been used into the field of casting alloy strength.In this paper, optical microscopy, mechanical testing, scanning electron microscopy, corrosion immersion test, electrochemical tests, X-ray diffraction analysis, thermal analysis, and transmission electron microscopy methods have been taken for ZA27 alloy that with different amounts of modified superfine SiC powders. Microstructure, mechanical properties and corrosion resistance as well as modification of its mechanism of modified superfine SiC powders were studied.The results show that: After adding the modified superfine SiC powders, the microstructure of ZA27 alloy is refined. When the amount of modified superfine SiC powders is 0.5%, ZA27 alloy exhibits excellent mechanical properties and corrosion resistance. The tensile strength and elongation are increased by 21.94% and 16.7%. In the 2% H2SO4 solution and 5% NaOH solution of room temperature, the corrosion rates of ZA27 alloy are decreased by 14.28% and 20.45%. Electrochemical experiments in 3.5% NaCl solution of room temperature, the corrosion potential of ZA27 alloy increased 2.78%. Analysis from the experiment, modified superfine SiC powders get clean surface due to the fall of SiO2 film that formed on the surface of SiC. The clean surface can reduce the wetting resistance between ZA27 alloy and SiC. So the modified superfine SiC powders play the role of heterogeneous nucleation core and increase the nucleation core. As a result, the microstructure of ZA27 alloy changes from the thick branches into equiaxed grains and small homogeneous rose-shape crystal. Also the eutectic lamellar spacing has been reduced. At the same time, the modified superfine SiC powders as the second phase particles in the matrix play the role of toughness in the ZA27 alloy. Analysis of EIS and XRD, the modified superfine SiC powders promote the surface of ZA27 alloy form a protective film that has better blocking effect of corrosion. So the corrosion resistance of ZA27 alloy has been improved.