INFLUENCE OF PARTICLES WITH DIFFERENT SIZES ON MICROSTRUCTURE, TEXTURE AND MECHANICAL PROPERTIES OF Al-Mg-Si-Cu SERIES ALLOYS

To reduce the weight of car body, Al-Mg-Si-Cu alloys have been used to produce outer body panels of automobiles due to their relatively good formability in the solution treated condition and high strength in the age hardened condition. However, their formability is significantly poor compared to that of steels, which are the major drawbacks to wide-scale application of aluminum in the automotive industry. The microstructural characteristics developed during recrystallization, most notably grain size and crystallographic texture, play a dominant role in controlling the mechanical properties and formability of sheet in the T4 condition. In this work, the effect of particles with different sizes on the mechanical properties, microstructure and texture of Al-Mg-Si-Cu alloys was studied through tensile test, OM, SEM, TEM and EBSD measurement. The results reveal that with increase of solute concentration, the average plastic strain ratio (r) over bar, yield strength and ultimate tensile strength increase, but the elonga- tion decreases and with different extents in the three directions. In addition, the number of observed particles with different sizes in the alloy matrix such as Mga Si, Al15Mn3Si2 and alpha-Al(Fe, Mn)Si phases also increases. When the size and concentration of these particles are controlled appropriately, lots of finer recrystallized grains can form during solution treatment due to the particle stimulated nucleation (PSN) effect of coarse particles and pinning effect of finer particles. The main texture components include CubeNDis, Goss{011}< 100 >, P {011}< 122 > and Cu{112}< 111 > for the alloy with fine-grained structure. At last, according to the relationship among alloy composition, thermomechanical processing and microstructure, the model of nucleation and growth of recrystallized grains affected by the particles with different sizes was also proposed.