Influence Of Mn For Microstructures And Mechanical Properties Of The New High Strength Al-Mg-Si Alloy

The paper optimizes the alloy component that is based on aluminum alloy6069. In order to develop a new type of alloy material, some ways are used including adding the element of Mn as well as changing the contents of Si, and adopting the reasonable smelting and heat treatment process. Meanwhile, the influences of Si, Mn for microstructures and properties of the new Al-Mg-Si alloy are systematically studied by using transmission electron microscope, SEM, X-ray diffraction, high resolution electron microscopic and other analysis test means. And the exist forms and mechanism of the adding elements in the alloys are discussed preliminarily.The paper has carried on the preliminary discussion about the extrusion process and heat treatment behavior of the new deformation aluminum.The heat treatments include homogenization annealing, solid solution treatment and aging treatment. This paper investigaites the mechanical properties and microstructure of alloys with different additions, which are dealed with the same heat treatment condition, in order to find out a better component of the alloy. According to DSC analysis and some literatures, it is known that homogenization treatment is to heat the alloy at560℃for24hours. T6heat treatment process for the extrusions are to solute it at560℃for2hours, then to age it at170℃for12hours immediately after being water quenched. This heat treatment can make the extrusions get an excellent combination between strength and plasticity. According to the capability of the equipment in the laboratory, the extrusion process is determined as follows:the temperature of extrusion is430℃. The biggest force of extrusion is120MPa, and the extrusion ratio is14.7.Mg/Si=1.73, the mechanical properties of the alloys can be improved but not significantly by means of changing the content of Mn. When the content of Mn is reached up to0.2%in the alloy, the mechanical properties of the Al-Mg-Si alloy is higher than that of other alloys with different contents of Mn additions.Tensile strength, yield strength and elongation of extrusion after heat treatment, respectively can be up to425MPa,365MPa,17.7%. When the content of Mn is too high, the massive MnAl6phase which can reduce alloy mechanical properties will be found.Mn and Si combination will form AlFeMnSi phase, AlFeSi phase or AlMnSi phase in the alloy, these phases can make the lack of Si. The mechanical properties of the alloy can not be improved significantly either when both the contents of Si and Mn are added into the alloy, which let the Mg/Si<1.73. However, when the content of Mn has reached up to0.2%, the mechanical properties of the alloy are improved most. The tensile strength, yield strength and elongation of this extrusion after heat treatment are431.4MPa,368.7MPa,15.7%respectively.