Study On The Micro-structures And Mechanical Properties For 2519 Al Alloy

2519 Al alloy is a kind of heat treatment strengthening aluminium alloy, there has the intimate relation between internal microstructure and alloy’s property. With thermal treatments, the alloy’s microstructure and mechanical properties change. The article is a systematic study about changes of 2519 Al alloy’s microstructure and mechanical properties with the thermal treatments: homogenizing heat treatment, thermal extrusion deformation, solution treatment and artificial ageing. The research methods include HV hardness test, intensity measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-annular dark field (HADDF). The study mainly includes:The alloy’s microstructure was evolving with thermal treatment, the result shows that there is serious dendrite segregation existing in the 2519 Al as-cast alloy, the alloy elements congregate in grain boundary, formed the eutectic phases Al2Cu and Al7Cu2Fe, lots of air bubble existed in as-cast alloy, the as-cast alloy’s tensile strength is 129.3MPa and the stretching ratio is 1%. With homogenizing heat treatment, the alloy element Cu dissolved into Al matrix, the alloy’s property is improved, the tensile strength is 286.8MPa and stretching ratio is 5.4%. The subsequent thermal extrusion deformation, the shape of grain is changed from axis-equal to strip, the alloy’s tensile strength is 329.9MPa and stretching ratio is 21.8%, the property has a large improvement. With supersaturated solid solution at 530℃for 1 hour, the element Cu supersaturated into Al crystal, the alloy’s tensile strength is 346.1MPa and stretching ratio is 24.5%. When the supersaturated sample was artificial aged at 180℃for 12 hours, and then the strengthen nano-precipitate formed, the main plate precipitateθ′phase and lath precipitate S phase, the evolution between GPⅡzone andθ′phase and theθ′phase growth mechanism are investigated using HADDF. The plate-precipitateθ′phase at over-aged stage was observed using SEM and number density was measured accurately,. The increasing of precipitates’size and decreasing of number density and the volume fraction ofθ′phase were described. The S phase has two nucleation mechanisms was proposed, including heterogenous nucleation and homogeneous nucleation. The alloy’s hardness has a significant age-hardening behavior with ageing time, the hardness-time curve can be divided into three stages: under-ageing status, peak-ageing status, over-ageing status. The peak-aged alloy’s tensile strength is 396.8MPa and stretching ratio is 10.2%. The different heat treatment alloy’s microstructure and fracture mode was analysis, and an optimization of heat treatment was proposed, the alloy’s mechanical properties were improved with tensile strength is 464MPa and stretching ratio is 10.6%.