In-situ Formation Of Tib₂ Particle By Elta And The Effect Of The Particle On The Microstructure And Properties Of Al Alloy

In recent years , LSM technique has extensively been used to prepare aluminum-matrix composites, and many different kinds of aluminum-matrix composites with well-distributed fine TiB₂ particles (<1μm) and good mechanical properties have been produced using this technique. However, there are some defects in the technique. For example, the TiB₂ particles formed are easily wrapped by the salt film, which probably contaminate the interfaces between the TiB₂ particles and aluminum-matrix and impaire the reinforcing effect of the TiB₂ particles. Besides, LSM technique has yet the disadvantages of low utilization ratio of raw materials and polluting environment. In this paper, a new method of in-situ formation of TiB₂ particle by adding Al-B master alloy to electrolytic low-titanium aluminum (ELTA) melt to prepare TiB₂/Al alloy has been put forward, and some studies on it have been done. The main studying results are summarized as follows:Firstly, the feasibility of adding Al-B master alloy to the ELTA melt to prepare TiB₂/Al alloy was investigated, and the HB hardness of the prepared TiB₂/Al alloys containing different content of the TiB₂ particle was also measured. The results show that the new method is feasible. And the TiB₂ particles formated in the melt are very small and evenly present in the melt because of even distribution of the titanium atom in the ELTA. With the increase of the content of the TiB₂ particle in the alloy, the HB hardness of the TiB₂ /Al alloy is obviously increased.Secondly, the effect of the temperature on the formation of TiB₂ particle in the melt was investigated. The results indicate that agglomeration of the TiB₂ particle formed is weakened with the increase of the melt temperature from 750℃to 950℃. As a result, the TiB₂ particles becomes much finer and are distributed in the melt more uniformly, The HB hardness of the TiB₂/Al alloy is also increased. However, more Al₃Ti particles will be formed at high melt temperature, which will decrease the mechanical properties of the alloy. So the melt temperature should not be too high. The optimal temperature of preparing the TiB₂/Al alloy using the new method is about 850℃.Thirdly, the effect of excessive Ti on the microstructure of the TiB₂/Al alloy was investigated. The results show that excessive Ti may have a certain refinement effect onα-Al in the alloy. The TiB₂ particles formed are yet distributed more uniformly in the alloy due to the fineα-Al grain of the alloy. Also, the HB hardness of the alloy is increased to some extent.Fourthly, the effect of Mg element on the agglomeration of the TiB₂ particle formed in the TiB₂/Al alloy melt were studied. The results prove that adding Mg to the melt can decrease the agglomeration of the TiB₂ particles, so the TiB₂ particles become much finer and more well-distributed in the melt. The HB hardness of the Al alloy is also increased at the same time. Moreover, the Mg element can yet improve the wettability between the TiB₂ particle and Al matrix, which is beneficial to the mechanical properties of the alloy.Lastly, the Al-Si-Mg alloys with different content of the TiB₂ particle were prepared using the ELTA, Al-B master alloy, Si and Mg etc. And the in-situ formation of the TiB₂ particle in the Al-Si-Mg alloy melt and the effect of the particle on the microstructure and mechanical properties of such alloy were investigated. The results have shown that preparing applied alloy with TiB₂ particles using the new method is basically feasible. With the increase of the content of the TiB₂ particle formed, the strength of the Al-Si-Mg alloy decreases, but the plasticity obviously increases. The comprehensive mechanical property of the alloy is improved.