Study On The Structural Relationship Between The Liquid And Solid And Solid Resistivity Of Al-Mg-Si Alloy

The structure of the liquid, supersaturated solid solution and amorphous Al85Mg10Si5 and Al185Mg1Si14 alloy are investigated by ab initio molecular dynamics simulation. The partial pair correlation functions, partial coordination number and chemical short range order are used to investigate the alloys. The resistivity of Al-Mg-Si alloy in the heating process is measured by using the high temperature and high precision resistance measurement system, and it compares the results with differential scanning calorimetry (DSC), which makes the good arrangement in the above two methods.Structural analysis on the AlssMgioSis alloy shows that Al-Si and Mg-Si chemical short range orders are dominant in the liquid, supersaturated solid solution and amorphous systems. The interaction of Mg and Si unlike atoms is the strongest and they tend to form the Mg-Si unlike atom clusters. Si atoms are separated from each other, so that it is more difficult for them to aggregate in the Al85Mg10Si5 supersaturated solid solution than in liquid alloy. In other words, the chemical short range order in supersaturated solid solution is a little better than that of liquid. The value between the first and second peaks of Al85Mg10Si5 amorphous alloy’s gsisi(r) curve is zero, which indicates Si atoms are separated from each other, or they directly form separated Si-Si atom clusters. The second peak of gAlAl(r) curve in Al85Mg10Si5 amorphous alloy appears splitting, which represents the characteristics of amorphous alloys.Al-Mg chemical short range orders are the main chemical short range orders in the Al185Mg1Si14 liquid, supersaturated solid solution and amorphous alloys by the analysis of partial pair correlation functions, partial coordination number and chemical short range order. Si atoms are more likely to separate from each other in the Al185Mg1Si14 alloy than the Al85Mg10Si5 alloy. The second peak of gAlsi(r) curve in Al185Mg1Si14 amorphous alloy appears splitting, which shows that Al185Mg1Si14 alloy appears amorphous phase in the process of rapid solidification.The resitivity is sensitive to the organizational structure of the metal and alloy, and it can effectively reveal the change of structure, so the change of resitivity of Al-(0.3-0.4.wt%)Mg-7.wt%Si alloy is tested by the high temperature and high precision resistance measurement system in the process of heating. The resitivity of Al-Mg-Si alloy bar in the heating process can be divided into three stages:the resistivity of alloy increases as the temperature increase; then resistivity almost no longer increase with the temperature rise, finally the resistivity increases as the temperature increase. Comparing with pure aluminum bar, pure aluminum wire and Al-Si alloy bar, Al-Mg-Si alloy appears almost unchangeable resitivity in the second part. There are two reasons for this phenomenon. On the one hand, the speed of diffusion of atoms and vacancies is enhanced in the heating process and vacancies are captured by Si and Mg atoms. So the electronic scattering decreases and the resistance of Al-Mg-Si alloy decreases. On the other hand, the resistance of aluminum-base alloys linearly increases with tempreture. The resitivity of the high purity Al-Mg-Si alloy is smaller than the low purity alloy, since the high purity alloy contains fewer impurities than the low purity alloy, and the effect of electron scattering is weak.Furthermore, the Al-Mg-Si alloy, Al-Si alloy, pure aluminum bar and pure aluminum wire were measured by DSC. The resistivity of the second part of Al-Mg-Si alloy indicated by the high temperature and high precision resistance measurement system is matched very well with that indicated by DSC method in a reasonable error range. The obvious exothermic peak shows that atom vacancies are captured by Mg and Si atoms in the alloy, which makes the arrangement of atoms in the Al-Mg-Si alloy more orderly than before. While the DSC curves of pure aluminum rod and pure aluminum wire don’t appear any exothermic and endothermic peak in more than 200℃. There is an exothermic peak in Al-Si alloy, which is similar to Al-Mg-Si alloy beacause some vacancies in the alloy are captured by the silicon atoms.