Atomistic Study On The Interaction Of The Edge Dislocation With Alloy Elements In Aluminum Alloys

With the development of the automobile industry and the urgent requirement of the automobile light weight, it attracts more and more attention on studying which facters influence the strength and plastic formability of aluminum alloys used in car body. The dislocations play an important role in the plastic deformation process of crystalline materials. The characteristics of the dislocation can directly associate with the macro scopic mechanical properties of the material. The elements added in aluminum alloys can interact with the dislocations and influence their movement during the plastic deformation process, resulting in an improvement of the mechanical property of aluminum alloys. Molecular dynamics simulations with the modified embedded atom method (MEAM) were used to study the interaction between the Al edge dislocation and the Mg, Si, and Fe dopants in the alloy. At the atomic scale, the present work sheds light on the strengthening effects of the alloying elements in the Al alloys. This thesis mainly consists of the following parts.(1) The history of the dislocation theory is simply introduced in this article at first, and the knowledge about the theoretical models of the dislocation is illustrated in detail. Then the article introduces the knowledge of molecular dynamics simulation, and the potential function and algorithm in the simulation are introduced.(2) We employed the MEAM potential function for the Al、Mg、Si、Cu and Fe alloys which was given by B. Jelinek in his paper published in 2012. We calculated the lattice constants of aluminum, magnesium, silicon, iron crystals. We also calculated other properties like the bulk modulus with the MEAM potential. We compared the calculated value with the experimental value to verify the accuracy of the MEAM potential. We calculated the melting points of pure aluminum and pure magnesium which were TAl=1090K and TMg=790K with the potential by the solid-liquid co-existing simulations. These tests ensure that the MEAM potentials are sufficiently reliable for our simulations.(3) The Peierls-Nabarro model was used in the present study. We used a program written by Fortran language to build the edge dislocation model of aluminum alloys for our simulation. And the model accords with the stress-strain relationship and lattice structure of the Peierls-Nabarro model theory.(4) Molecular dynamics simulations were used to study the interaction between the Al edge dislocation and the Mg, Si, and Fe dopants in the alloy. The calculated results show that Mg, Si, Fe atoms tend to gather around the dislocation in the Al alloy. Compared with Fe, the interactions of the edge dislocation with Mg and Si are stronger, so Mg and Si have a better solid solution strengthening effect in this alloy.(5) In order to clarify the influence of alloy elements aggregation on the mechanical properties of aluminum alloys during the aging process, we have studied the interaction of the dislocation with the Mg clusters. We find that large clusters in aluminum alloys have a stronger interaction with the dislocations. The large clusters can obviously draw the dislocations and inhibit their movement, resulting in a better pinning effect.