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1、95Microstructure and Mechanical Properties of Purity AluminumRefined with Salt Containing Ti and B ElementsHenghua ZHANG, Xuan TANG, Guangjie SHAOand Luoping XUThe microstructure and mechanical properties of purity aluminum refined with salt con- taining Ti and B elements have been studied in detail
2、 with Optical Microscope and MTS (Mechanical Testing and Simulation). The salt containing weight ratio of 22.2Ti:1B has themost refining effect on the purity aluminum with the finest structure and the best mechanical properties, meanwhile it also possesses the advantages of short reacting time (with
3、in 5 min-utes) and long fading time (more than 20 hours). The refining effect of the salt increases withthe content of Ti and B in the melting and the refining mechanism is mainly contributed to theheterogeneous nuclei of more fine TiAl3particles dispersed in the melting, which come from the reactio
4、n between the salt and aluminum. Purity B contained salt has little or no directlyrefining effect, However, B contained salt has indirect refining effect on the purity aluminum when it is added simultaneously with Ti contained salt, this may be due to that the dispersiveand fine boride (TiB2) could
5、be taken as the heterogeneous nuclei for TiAl3particle, and then prevents the coarsening of the TiAl3particle.Key Words:Purity Aluminum, Structure and Mechanical Properties, HeterogeneousNuclei, Refining Mechanism1.IntroductionMechanical property of purity aluminum can be im-proved by alloying or re
6、fining method, especially by thechemical refining. Chemical refining is sometime moreconvenient and necessary. The conventional refiners are mainly the master alloy of Al-B, Al-Ti, Al-Ti-B, and Al- Ti-C etc.(1)(9)In addition, Al-Ti-C-Re and Al-Ti-B-Re are also reported(10)(13). However they still ha
7、ve theirown deficiencies. It needs to design addition processesto achieve the most effective grain refinement. Such as,qualification master alloys must be prepared firstly, and sometimes, the master alloys had better to be changed into smaller size or powder by deformations to obtain moreeff ective
8、refinement(3),(4),(6),(7). Finding the contact timewith the finest grain refinement (critical contact time) is another problem. If the contact time is much too short, thefinest grain size may not be achieved. On the contrary, ifthe contact time is much too long, the grain refiner will be faded(14).
9、Meanwhile, the essential refining mechan-Received 16th May, 2005 (No. 05-5049) School of Material Science and Engineering, Shanghai University, Box15, Shanghai University, 149 Yanchang Road, Shanghai 200072, China. E-mail: ism and fading mechanism are still unclear or inconsis- tent(1)(9),(14),(15).
10、If salt refiner containing Ti and B elements was di-rectly used to refine the aluminum, it can save much time and cost, comparing with the addition of the master alloy contained same elements. However, there are a few papersconcentrated on this field and exist many problems to besolved, such as cont
11、acting and fading time, refining and fading mechanism etc.(16),(17)In this study, the effect of salt containing Ti and B elements on the purity aluminumwas studied in detail. Meanwhile the refining mechanism was also investigated by SEM-EDAX and thermodynam- ics calculation.2.Experimental ProcedureC
12、ommerciallypurealuminumwithmorethan 99.9wt%Al was served as experimental material, and commercially pure K2TiF6salt, KBF4salt and mixtures of K2TiF6and KBF4with various weight ratio of Ti/B (saltmixtures) were servedas refiners. The particle size of salts is about 75m and the purity is more than 99.
13、0wt%. Purity aluminum was molten in Al2O3crucible with resistant furnace to 750C. Salt mixtures with different ra-tio of Ti/B and different contents were added to the molten aluminum. After manual stirring, removing slag and dif- ferent holding time, the molten aluminum was cast intoJSME Internation
14、al JournalSeries A, Vol.49, No.1, 200696iron mould, and it was preheated to 200C before cast- ing(16),(17). Samples were cut along transversal section and 20mm apart from the ingot bottom, then grounded and polished. Macrostructure were etched in acids mixture of 5mL HF-40%, 75mL HCl-38%, and 25mL H
15、NO3-68% and recorded with digital camera. Microstructure were etched in 4%HF solution and recorded with Nikon-L150 OpticalMicroscope. Mechanicalpropertiesofthesamples were measured by MTS and three measured values were averaged as results. Optical Microscope and JSM-6700F scanning electron microscop
16、e with EDAX were used to observe the size and constitution of the heterogeneous nu- clei in -Al grain. Thermodynamic calculation and analy-sis were used to investigate the refining mechanism.3.Results and Discussion3.1Effect of Ti/B ratio on the macrostructure and properties Figure 1 shows the typical macrostructure of the pu-rity aluminum refined by salt mixtures with different ra- tios of Ti/B, which was held 30 minutes after added to the melting. The
