Influence Of Nano TiN/Ti Refiner On The Microstructure And Properties Of Pure Al And Al-4Cu Alloy

In the common techniques of grain refinement, adding ultra-fine ceramic particles asnucleation particles can provide a large number of dispersed particles in order to promoteheterogeneous nucleation, and the particles can refine the structure of aluminum and itsalloys in the process of solidification and rolling deformation. This method has goodcontrollability, and can overcome the method of endogenous particle in uncertainty anddifficulty to control the number and size of particles generated, which is suitable forindustrial production and gradually attracts considerable attention of domestic andinternational scholars. However, because of the poor wettability between adding particlesand liquid metal, the development of this technology was restricted. Thus, it’s significantto improve the wettability and enhance nucleating effect for refining the structures ofaluminum alloys and make the most advantage of this method.A novel 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 in commercial pure Al were investigated, the refinement mechanism of which wasalso discussed. The influence of the prepared grain refiner on pure Al weld refinement andinhibition of grain thickening in the recrystallization process of pure aluminum afterdeformation and damping properties were analyzed as well. On this basis, the effects ofthe refiner on Al-4Cu alloy grain refinement and microstructures and properties aftersolution and aging treatment were studied, and the effects of nano TiN particles on Al-4Cuaging process was discussed. The following results were obtained.The TiN/Ti composite refiner exhibits excellent grain refining effects on commercialpure aluminum. The microstructures of sample is transformed from coarse columnar grainzone and centre coarse equiaxed zone of the sample without refiners into fine equiaxedgrain zone with0.2wt%TiN/Ti addition, which is better than Ti. The result of TEM showsTiN reveals perfect coherent relationship with Al matrix and exhibits excellentgrain-refining efficiency as nucleation particles because adding Ti particles helps improvethe wettability between TiN and aluminum alloy melt.With0.2wt%addition of TiN/Ti grain refiners, the structures of the weld are mainlyfine equiaxed grains, which show TiN particles can inhibit growth of columnar crystalseffectively. TiN/Ti composite refiner has a positive effect on controlling the grain size in the process of recrystallization. After recrystallization treatment after deformation, thehardness of sample with0.2wt%TiN/Ti is higher than the hardness of sample withoutgrain refiners and with0.2wt%Ti addition, and the TiN particle inhibit growth of grainsduring the heat treatment.In the smaller strain amplitude, the damping curves of three samples are thedislocation damping-strain spectrum, and dislocation internal friction plays a dominantrole. The damping performance of sample with0.2wt%TiN/Ti addition is better than thatof the other two samples. In large strain amplitude, the damping curve of three samples isbasically the same.TiN/Ti composite refiner exhibits the excellent grain refining effects on as-castmicrostructure of Al-4Cu alloy. TiN/Ti composite refiner can significantly refine theα-phase, and with0.2wt%addition, average grain size of Al-4Cu sample decreases from161μm to131μm, shows better grain refining effect than that of pure Ti refiner. AddingTiN particles facilitate the precipitation of metastable phases of q ’’and q ’and the timeneeded to reach peak aging is shortened in the sample with0.2wt%TiN/Ti additioncompared with the samples without grain refiners and with0.2wt%Ti addition. Themicro-hardness of the aged sample added0.2wt%TiN/Ti refiner was the highest andreached its hardness peak-125HV, which increased by19%than that of the samplewithout any refiners. Comparing with the sample without adding grain refiners, the tensilestrength and yield strength of the sample with0.2wt%TiN/Ti refiner increased by103.1%and155.4%, respectively. By comparison, the fractures of the sample without any refinershad mixed-rupture characteristics of quasi-cleavage and dimples and the fractography ofthe fractured faces of the sample with0.2wt%TiN/Ti refiner exhibited ductile fracturewith dimples.