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Laser powder bed fusion (LPBF) has been demonstrated as a metal additive manufacturing technique that can manufacture high-performance metal components with complex shapes directly from raw powder materials. Although 18Ni-300 maraging steel has been extensively employed in this process, a significant trade-off has always existed between strength and ductility when using traditional solution and ageing heat treatments. This study addresses this problem by introducing a heat treatment combination that includes hot isostatic pressing (HIP) before the conventional ageing treatment. The experimental results demonstrated an enhancement of the relative density from 99.6% in the as-built conditions to 99.96% after HIP, although a small number of residual gas pores remained. The subsequent ageing treatment after HIP had a negligible effect on the reopening of these closed defects. Microstructure observations revealed that a fully martensitic structure can be obtained after HIP, and austenite reversion was less sensitive with the HIP + ageing treatment (HAT) compared to direct ageing treatment (DAT). Grain growth and alloying homogenisation also occurred during HIP. Massive nanoscale precipitations were formed both after DAT and HAT; quantitative analysis based on TEM observation indicated that the size of these precipitates was larger after subjecting to HAT. The room-temperature ultimate tensile strength and elongation to failure after HAT were approximately 6% and 100% higher than DAT, confirming the simultaneous enhancement of the strength and ductility after HAT. The findings of the present study offer insights into heat treatment approaches that can overcome the strength-ductility trade-off of LPBF-manufactured 18Ni-300 maraging steel, while also providing an alternative strategy for obtaining the simultaneous improvement of strength and ductility through heat treatments.

The flow behavior, microstructure evolution and softening mechanism of an AA7085 aluminum alloy are investigated by isothermal hot compression tests at 450 °C with the strain rates of 0.001 s−1 and 0.1 s−1. Optical microscopy (OM), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) are used to characterize microstructure evolution during deformation. The results reveal that the flow stress curves exhibit a single peak and then two types of flow stress curves are found in the present study. Microstructure characterization reveals that dynamic recovery (DRV) and recrystallization (DRX) occur in the both conditions. The microstructure discrepancy becomes significant with increasing strain rate after a certain strain level (e≥0.3). In the case of 0.001 s−1, the dynamic recovery is thought to precede continuous dynamic recrystallization. As the strain rate increased, the absence of dynamic recovery provides enough stored energy for discontinuous dynamic recrystallization (DDRX), resulting in a retardation in the occurrence of continuous dynamic recrystallization (CDRX).

The 2195 alloys prepared by traditional casting and spray forming technology were investigated by using X-ray diffraction, X-ray microscopy, electron probe microanalyser, scanning electron microscopy, transmission electron microscopy and tensile testing. The results show that the as-cast alloy consisted of large-scale grains with small amount of pores, while the as-sprayed alloy is composed of mainly fine equiaxed grains with abundant pores. In the grain boundary, continuous secondary phases (Al–Cu–Mg phase, Al–Cu phase, and Al–Cu–Fe phase) exist in the as-cast alloy, while semi-continuous/discontinuous secondary phases (Al–Cu phase and Al–Cu–Fe phase) present in the as-sprayed alloy. The main phases in the grain interior of the as-cast alloy are T1 (Al2CuLi), TB (Al7·.5Cu4Li) and σ (Al5Cu6Mg2) phases while T1 and TB phases for the as-sprayed alloy. The same homogenization treatment shows more solute contents dissolved in the spray formed 2195 alloy. The as-sprayed alloy has advantage of 35% in ultimate strength, 26% in yield strength and 54% in elongation compared to the as-cast alloy, respectively. This detailed studies manifest that subsequent processes of deformation and heat treatment for spray formed alloy need to be tailored based on its featured microstructure, compared with that of traditional cast alloy.

The natural aging and artificial aging behaviours of Al-Mg-Si-Cu alloys with different Mg/Si ratios and Cu additions were investigated using Vickers microhardness measurements, differential scanning calorimetry (DSC) analysis and transmission electron microscopy (TEM) characterisation. Excess Si and Cu additions enhanced the alloy hardening ability during natural (NA) and artificial aging (AA). Alloys with low Cu and high Si contents exhibited higher precipitation hardening than alloys rich in Mg during artificial aging. In contrast, the alloys with high amounts of Cu were less dependent on the Mg/Si ratio during precipitation hardening due to their similar aging kinetics. The main precipitate phases that contributed to the peak-aging hardness were the L, Q′ and β″ phases. In the over-aging conditions, the alloys rich in Mg and Cu had finer and more numerous precipitates than their Si-rich equivalents due to the preferential precipitation of the L phase. The combination of excess Mg and high Cu resulted in an alloy with a relatively low hardness in T4 temper and a relatively higher hardness after the paint baking cycle. Thus, this alloy has good potential for use in auto body panel applications.

The isothermal deformation compression tests of AA7085 aluminum alloy were performed on Gleeble-1500 system in the temperature range from 250 °C to 450 °C and at strain rate range from 0.01 s −1 to 10 s −1 . The microstructure of samples was observed using optical microscopy (OM) and transmission electron microscopy (TEM) techniques. The results show that the peak stress levels decreased with the increase of deformation temperatures or the decrease of strain rate, which can be represented by the Zener–Hollomon parameter in the exponent-type equation with the hot deformation activation energy of 249.11 KJ/mol. Dynamic recrystallization more obviously occurred in the sample with higher Z value than in the sample with lower Z value. Dynamic recrystallization is sensitively dependent on the deformation temperature.