Strengthening mechanism of cast heat resistant aluminum alloy

According to the high temperature strength theory of metals, with the increase of temperature, the strength of grain boundary decreases significantly, which makes the grain boundary become the weak link at high temperature. The plastic deformation mechanism changes from low temperature sliding to high temperature diffusion deformation, and the fracture mode changes from transgranular fracture to intergranular fracture. The deformation characteristics, strengthening mechanism and effect of the alloy at different temperatures were studied.

At low temperature, the deformation of the alloy is mainly characterized by dislocation slip and twinning. At this time, fine grain strengthening, deformation strengthening, solid solution strengthening and second phase strengthening (dispersion strengthening and precipitation strengthening) work together to improve the strength of the alloy. However, with the increase of temperature, the effect of all the strengthening mechanisms decreased. When the temperature reaches about 200 ℃, the deformation strengthening caused by plastic deformation due to dislocation recrystallization disappears; When the temperature reaches about 250 ℃, the precipitated transition phase grows up, leading to coarsening of the size, and changes from metastable state to stable state (such as GP region θ Juehe θ Change to θ- The results show that there is no coherent relationship between al2cu and matrix, and the effect of precipitation strengthening is basically ended; When the temperature rises to 300 ℃, the grain boundary becomes the weakest part of the alloy, and a large number of grain boundaries caused by fine grain strengthening become the source of the decrease of high temperature strength of the alloy; When the temperature is further increased to 350 ℃, the solution strengthening of lattice distortion caused by thermal diffusion is basically lost, and the coarsening of dispersed phase occurs mostly, resulting in the decrease of dislocation and pinning effect of grain boundary. Therefore, it is of great scientific significance and application value to explore the new high temperature strengthening mechanism of aluminum alloy and develop new microstructure control process.