The Limited Performance Of Grain Refinement For Aluminum Alloys Inoculated By Grain Refiners

Nowadays, with increasing demand on aluminum alloys with high quality, how to significantly improve the comprehensive mechanical properties becomes an urgent problem. It is an effective way to achieve a fine equiaxed grain structure and improve the comprehensive mechanical properties of aluminum products through additions of grain refiners. At present, Al-Ti-C(B) master alloys are the most widely used grain refiners for aluminum alloys in industries, thus it is necessary to take further detail research to study their grain refining performance on aluminum alloy.The present study researched the grain refining performance of Al-Ti-C(B) master alloys on the 1060,6063 and 772.0 aluminum alloys under the background of industrial applications, and then revealed the common regular pattern of aluminum grain refinement by proposing a concept of "grain refinement limit" and discussing its possible mechanisms. In addition, the influence of grain refinement on mechanical properties of 6063 alloys including the tensile strength, toughness, hardness and corrosion resistance were investigated, and then the correlation between grain size and mechanical properties was revealed in the present article. Furthermore, the influence of grain refinement on heat treatment of 6063 alloy was also studied. There is a great significance for this study of the grain refinement limit and the common regular pattern between grain refinement and mechanical properties of aluminum alloys. The major research results of the present work are as follows:(1) Grain refinement limit of aluminun alloys inoculated by Al-Ti-C(B) master alloysIt is revealed that there is a similar grain refinement limit of 1060,6063 and 772.0 aluminum alloys inoculated by Al-Ti-C(B) master alloys under the present experimental condition, which is about 40～50μm when the addition of Al-5Ti-0.25C master alloy is 1.5～2.0 wt.% or the addition of Al-5Ti-1B is 1.5～3.0 wt.%. It can be seen that the strict of Ti diffusion lead to the grain refinement limit, besides, the recalescence process occurring upon heterogeneous nucleation and many other factors will also influence the appearance of the grain refinement limit of aluminum alloys.(2) Influence of ultrasonic treatment on the microstructure and grain refining performance of aluminum alloysThe present work researched the Influence of ultrasonic treatment on the microstructure of Al-5Ti-0.25C master alloy and the grain refining performance of it on 6063 alloy. It shows that ultrasonic treatment can largely promote the diffuse distribution of TiC particles and crush the plate-like TiAl3 effectively, and then advance the dissolution of Al-5Ti-0.25C in aluminum melting. In addition, the average grain size of 6063 alloy can be refined from several millimeters to about 250μm under the ultrasonic treatment for about 1min, and the grain refinement limit of 6063 alloy was also decreased to 30μm.(3) Correlation between the grain size and mechanical propertiesThe mechanical properties of 6063 alloy were largely improved with the grain refinement. The highest ultimate tensile strength(UTS), toughness(Elongation) and hardness(HB) of 6063 alloy obtained by the refinement of Al-5Ti-0.25C and Al-5Ti-1B are 271MPa,15%,81.4 and 250MPa,16.5%,80, respectively. It is worthy to note that the mechanical properties of 6063 alloy refined by Al-5Ti-0.25C master alloy are always higher than that refined by Al-5Ti-1B. Furthermore, grain refinement can both increase the corrosion potential and decrease the corrosion current density and passive current density of 6063 alloy, and then improve the overall corrosion resistance of the alloy.(4) Influence of grain refinement on the heat treatment of 6063 alloyGrain refinement can accelerate the aging process of 6063 alloy and largely cut down its peak aging time. The peak aging time of the alloy will decrease continuously with the addition of Al-5Ti-0.25C master alloy increasing before reaching the peak. In fact, the peak aging time of the alloy will be shorten from 15h to 10-12h when the addition of Al-5Ti-0.25C is 1.0%.