| AlMgSiCu6000aluminum alloy with moderate strength, excellent formability and low density, has been widely used. In terms of industrial applications, the main research of this paper is focusing on the hardening, corrosion resistance and weldability of6005A alloys.The effect of T6and T6I6ageing treatment on hardness and intergranular corrosion properties and the joint of6005A-FSW of6005A aluminum alloy were investigated by hardness measurement, intergranular corrosion (IGC) test, electron backscattered diffraction (EBSD) analysis, transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) observation. The experimental results can be described as follows:1. Accelerated corrosion test revealed that the intergranular corrosion (IGC) of6005A was low susceptible in the beginning of artificial ageing after water quenching. However, IGC susceptibility increased and reached the peak hardness (120HV) by artificial ageing for12hours, with the average corrosion depth about100μm. Over ageing reduced the susceptibility of intergranular corrosion and introduced slight pitting.2. With T6I6ageing treatment, the density of precipitates inside the grain was higher than T6treatment. At the same time, the precipitates were still discontinuous along the grain boundaries, but the size of precipitates was larger than those of T6ageing treatment. Therefore, the T6I6ageing treatment for6005A aluminum alloy not only increased the maximum hardness (127HV), but also enhanced the intergranular corrosion resistance. The corrosion depth was only about30μm.3. IGC susceptibility in the T6peak ageing treatment was related to the micro-galvanic couplings between compounds on the grain boundary and the PFZ (Precipitate Free Zone). Pitting susceptibility introduced by over aging was mainly due to the coarsening of the second phase in the grain.4. Good mechanical properties could be achieved after FSW. The tensile strength and elongation of the FSW sample reached174MPa and9.0%, respectively, which were83.8%and79.2%of those of the matrix. The hardness distribution of the joint appeared as a shape of "W", and the thermo-mechanically affected zone was the weakest part in the joint.5. The matrix consisted fibrous grains, which was the typical miscrostructure in the6005A extruded state. Some recrystallized grains were observed, which were formed during hot extrusion process. There were three different parts in the joint. The heat-effected zone was almost the same with the maxtix which consisted of some growing grains and small amount of recrystallized grains. The grains in the thermo-mechanical affected zone further grew up and more recrystallized grains were formed; The welding nucleus zone was made up of fine recrystallized grains, dominating grain-boundary strengthening. The dimples in the matrix of6005A were big and deep while the dimples in the joint were small and shallow. The ductility of6005A-T4was better than the sample after FSW.6. The amount of β’-phase reduced from base zone (matrix) to the welding nucleus zone. In the welding nucleus zone, any β’-phase could be hardly found. There were no obvious changed in the Si phase. But due to recrystallization in the welding nucleus zone, the grain was greatly strengthened. Therefore, the hardness was higher than thermo-mechanical affected zone, which was the lowest in all the zones. |
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