| Aluminum alloys have small density, high specific strength, specific stiffness, goodflexibility, good shock resistance, corrosion resisting, highly conductive, high thermalconductivity, high recovery and regeneration rate, etc., which lead to a wider applicationin aerospace, weapon equipment and automotive fields. Grain refinement can increasemetal strength, toughness, and plastic observably, and it is also an important method ofimproving the comprehensive mechanical properties and processability of aluminumalloys. In the common techniques of grain refinement, adding ultra-fine ceramic particlesas nucleation particles can provide a large number of dispersed particles in order topromote heterogeneous nucleation, and the particles can refine the structure of aluminumand its alloys in the process of coagulation and rolling deformation. This method has goodcontrollability, and can overcome the method of endogenous particle in uncertainty anddifficult to control the number and size of particles generated, which is suitable forindustrial production. So, this method gradually attracts the attention of domestic andinternational scholars. However, because of the poor wettability between adding particlesand liquid metal, the development of this technology was restricted. If the wettability canbe improved, it is benefit to further reduce the content of alloying elements and improvethe strength and toughness of the metal, and economic value of this method is great.A new type of Ti cladding nano-sized TiN(TiN/Ti) composite grain refiner wasprepared by high energy ball milling, and effects of the prepared grain refiner on refiningeffects and anti-fading behavior in commercial pure Al were investigated, the mechanismof which was also discussed. The influence of the prepared grain refiner on commercialpure Al weld refinement and inhibition of grain thickening in the recrystallization processof pure aluminum after deformation were analyzed as well. Finally, the effects of therefiner on Al-4Cu alloy grain refinement and its performance after solution and aging treatment were studied. The following results were obtained.The TiN/Ti composite refiner exhibits its excellent grain refining effects oncommercial pure aluminum. With0.025%addition, micro structures of sample istransformed from coarse columnar into equiaxed one. With0.1%and0.2%addition,average grain size in the pure aluminum reaches up to146μm and82μm respectively.The grain effects of the TiN/Ti composite refiner are better than pure Ti and commercialAl-5Ti-1B refiner. TiN/Ti composite refiner exhibits good anti-fading performance in purealuminum within60min, the average grain size of which grows not more than30%. Theexcellent grain refining effects and good anti-fading performance are attributed to thedispersion and stability of nano-size TiN particles in pure aluminum.TiN/Ti composite refiner exhibits an obvious effect on refinement of commercialpure aluminum weld. With0.1%addition, the structures of the weld are mainly fineequiaxed grains, and the welding joint hardness is significantly higher. Not like the sampleadded0.1%pure Ti, the hardness of the weld center is still higher, and did not withdropping phenomenon. TiN/Ti composite refiner has a positive effect on controlling thegrain size in the process of recrystallization. For the pure aluminum samples with40%amount of compression and heat treatment at250℃for1.0h, the grains of the sampleadded0.1%pure Ti has an obvious thickening phenomenon. In contrast, oriented grains ofthe sample with0.1%TiN/Ti refiner addition cause by deformation have been eliminated,and there is not obvious grain thickening in the structure. In addition, new recrystallizedgrains form in boundary, which further refine the structure.TiN/Ti composite refiner can significantly refine the α phase of Al-4Cu alloy, andwith0.2%addition, average grain size of the Al-4Cu sample reaches up to152μm, whichis50%as the sample without any refiner. The sample added TiN/Ti composite refinerobtains47.5HBS in Brinell hardness test, which increases by10.7%than the samplewithout any refiner. TiN/Ti composite refiner can improve the performance of Al-4Cualloy after the solution and aging treatment. After aging treatment, the micro hardness of the sample added0.2%TiN/Ti refiner reaches106HV, which increases by20%than thesample without adding refiner. |
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