Effects Of Interrupted Ageing On Microstructures,Mechanical Properties And Impact Resistance Of Aluminum Alloy2519A

ABSTRACT:For further improving mechanical properties of aluminum alloy2519A, the interrupted ageing process was studied in this research. The effects of the interrupted ageing on microstructures and mechanical properties of aluminum alloy2519A were investigated by optical microscopy (OM), Vickers hardness-testing, scanning electron microscopy (SEM), transmission electron microscopy (TEM), split Hopkinson pressure bar (SHPB) and tensile tests, ballistic resistance test. The main conclusions are as follows:(1) Two interrupted ageing processes for aluminum alloy2519A were researched. The T8I6process is "Solution treatment, Quenching, Cold working, Pre-ageing, Interrupted ageing, Re-ageing" and the T9I6process is "Solution treatment, Quenching, Pre-ageing, Cold working, Interrupted ageing, Re-ageing". Compared with the traditional T87process, the T8I6process improved the elongation and toughness of the alloy obviously, which of the2519-T8I6alloy increased by more than90%, are17.5%and43.4MPa-m1/2, while there was no decrease in strength. The strength of the2519A alloy was increased by T9I6process markedly, the yield strength and tensile strength reached501.0MPa,540.1MPa, respectively.(2) The effect of the interrupted ageing on the microstructure was investigated. In the procedure at low temperature, Cu atoms segregated to a large amount of Cu-rich G.P. zones, while the rate of their migration speed reduced, thus uniformity of nucleation in G.P. zones was obtained. The G.P. zones which were the uncleation of the following ageing precipitated phases became denser and finer. These changes in the alloy laid the foundation for the enhancement in the properties of aluminum alloy2519A.(3) The effect of interrupted ageing on dynamic mechanical property of the aluminum alloy2519A was studied. After the analysis of all true stress-strain curves, the2519A-T916alloy had the highest dynamic yield strength and energy absorption ability regardless of the impact condition. At stain rate of5400s-1, the integrity of the specimen was kept well and no adiabatic shear bands were found. The strain rate sensitivity parameter of the2519A-T9I6alloy was higher than that of the alloy2519A with the other two temper. It could be concluded that the2519A-T9I6alloy had the best dynamic mechanical property. The dynamic mechanical property of2519A-T816alloy was lowere than2519A-T9I6alloy but higher than the2519A-T87alloy. It could be inferred that the improvement in fracture toughness, elongation and increasing in strength of the alloy created favorable condition for the enhancement of the impact resistance.(4) The ballistic resistance of the2519A-T9I6alloy thick plate was investigated. The plate with30mm thickness was shot obliquely by an incendiary projectile7.62mm in diameter. The ballistic limit velocity (V50) of2519A-T9I6aluminum plate was715m/s. Hardness was falling to that of the matrix metal with increasing distance from the crater, and the plasticity deformation region was within3.5mm around the ballistic area. The penetration process was divided into three stages according to microstructure character:instant contact stages, steady penetration stage and finished stage.