Research Of Strengthen Technology On Several Engineering Aluminum Alloys

Although the application of aluminum alloy in the industry is late, it has been developed into the second metal materials. In terms of auto lightweight, the application of aluminum alloy palys an important role. Using the casting aluminum alloy to replace the original steel material not only can ruduce the overall quality of car, but also can save energy. In other terms of deformation aluminum alloy, such as aluminum plate, strip, tube are widely used in construction, packaging and mechanical industry. At present, the development of aluminum alloy is limited due to the low strength, therefore, exploiting a new type of aluminum alloy with high strength become a hot research topic. One part of this paper study the effect of strengthing method on Al-Si alloys; another part is under the project of “The research of high strength aluminum plate” to study the the effect of strengthing method on Al-1.2Mn alloys.The mechanical propersities and microstructure of the alloy have been studied by means of metallographic microscope, SEM, EDS, XRD and tensie test. The effect of different strengthen technique on the microstructure and properties were studied.The composition of hypoeutectic Al-Si alloy is decided as Al-9Si-0.5Mg. By using DSC analysis, there are a certain structural transformation in the range of 855-885℃. Results show that different melt temperature in melt thermal-rate treatment（MTRT） have different effects on Al-Si alloy. When the Al-9Si-0.5Mg alloy is treated with MTRT by 930℃ melt for 20 min, then making the temperature of the melt drop rapidly to 760℃ for 10 min, the mechanical propersities of alloy reach the peak values, the tensile strength, yield strength, hardness and elongation increased by 24.3%、37.7%、82.9%、21.8% respectively compared with that untreated alloy. The α-Al changes into rod-like or equiaxial crystals, and eutectic silicon also changes into granular morphology.When added 0.2%Y into Al-9Si-0.5Mg alloy, the tensile strength, yield strength, hardness and elongation of alloy increased by 12.8%、17.2%、31.9%、9.6% respectively. Y elements adsorb on the growth steps to change the growth mode of Si, and eventually forms fibrous or granular eutectic silicon. According to the results of XRD and SEM for Al-Ti-B-Y master alloy, it exists TiB₂、AlB2、TiA_l3和 Ti4Al43Y6 phases. Each phase has the different mechanism of nucleation in alloy. After adding 3% Al-Ti-B-Y into the Al-Si alloy, the grains can be refined and the mechanical propersities cen be increased. the tensile strength, yield strength, hardness and elongation of alloy increased by 19.3%, 28.3%, 65.1%, 20.5% respectively。The combination of MTRT and refinement can improve the microstructure and mechanical propersities greatly. The experiment results show that the best treatment technique is: the alloy was first melted to 930℃, and held for 20 min, then making the temperature of the melt drop rapidly to 760℃for 10 min. The tensile strength, yield strength, hardness and elongation of alloy increased by 31.2% 、 22.6% 、 25.6% and 80.5% respectively. The microstructure of alloys also improved.Added Y and Al-5Ti-1B into Al-1.2Mn alloy can rafine the grains and increase the mechanical propersities, especially after adding Al-5Ti-1B, the α-Al changes into rod-like or equiaxial crystals and the size of second phase decreases. At the same time, the strength of Al-1.2Mn alloy improved slightly, but the elongation increase remarkably, i.e. the plasticity of alloy is better.After addin Mg, Si into Al-1.2Mn alloy the strength increased remarkably, but the elongation decreased sharply. When the addition of Si is high, Si and Fe will form the bone-like phase--α-Al12（FeMn）3Si, which worsen the propersities of alloy, so the addition of Mg and Si must be strictly control. In order to improve the plasticity, the author added Al-5Ti-1B into Al-1.2Mn alloy. Results show that added 0.5%Mg, 0.3%Si and 3% Al-5Ti-1B into Al-1.2Mn alloy, the tensile strength, yield strength, hardness and elongation of alloy increased by35.6%、28.1%、40.5% respectively. The strength of alloy increased greatly and the elongation still over 20%, so the each index of mechanical propersities reach the requirement. It is mainly because after adding Al-5Ti-1B into alloy, a large number of nucleation particles can be provided by TiA_l3 and TiB₂.