Influence of Ti and melt number on microstructure and mechanical properties of Al-Si alloy on agriculture machine parts
2018
Lipinski, T., University of Warmia and Mazury in Olsztyn (Poland)
Reducing the weight of the structure promotes improved machine performance and reduced fuel consumption. This can be achieved by optimizing the construction and use of light materials. It is the reason why aluminium is growing in popularity, mainly in the automotive industry and working machines, including agriculture. Al-Si alloys are still very popular mainly due to low density and high corrosion resistance. In order to reduce production costs, more and more machine parts are produced using the casting method. This favours the increase in the popularity of hypo-eutectic silumins. Among hypo-eutectic Al-Si alloys Al-9 %SiMg alloy is often used. Its raw microstructure consists of the plastic α phase and the large grains and needles of the undeformable β phase, which is the natural notch in the microstructure. This microstructure promotes the tendency to cracking the alloy. Through the modification process it is possible to fragmentation the beta phase and thus the plasticization of the alloy. By this method, the problem can be solved at the first melting. The market economy enforces the recovery of alloys and the use of waste from foundry production, such as risers, the gating system, castings with big defects, etc. It is then necessary to re-melt the alloy. It is uncertain whether the originally obtained microstructure, and therefore also the properties of the melts after a few melts, will not be adversely affected. Many salts and chemical compounds are used in the industry for modification. There is known modifying activity of such elements as: Na, Ca, K, Li, Ce, Te, Sr, Sb, Ti, B. Some of them have a permanent effect, but for most of them the effect of modification decreases with the time of holding the alloy in the liquid state and as expected, with the number of melts. With the number of melts also increases the holding time of the alloy in the liquid state. This paper presents the results of different ranges of Ti as a modification addition and melt number of the Al-9 %SiMg alloy. The effect of the Ti modifier on the microstructure, mechanical properties on the alloy was presented in graphs. As the research results showed the modifications of a hypo-eutectic Al-9 %SiMg alloy firstly improved the alloy’s properties, but with an increased number of melt the microstructure and mechanical properties were decreased.
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