The Characteristic of Fe as a β-Ti Stabilizer in Ti Alloys

It is well known that adding elements, especially β-Ti stabilizers, are holding a significant effect on titanium alloy strength due to the solution and precipitate strengthening mechanisms. In order to reveal the Fe strengthening mechanism in titanium, this study investigate the effect of Fe on the stability of β-Ti and the phase transition between α, β and ω phase with first-principle calculations. According to our study, Fe is a strong β-Ti phase stabilizer could owe to the 3d orbital into eg and t2g states which results in strong hybridization between Fe-d orbital and Ti-d orbital. The phase transition from ω to β or from α to β becomes easier for Fe-doped Ti compared to pure titanium. Based on our results, it is found that one added Fe atom can lead the phase transition (ω → β) of at least nine titanium atoms, which further proves that Fe has a strong stabilizing effect on β-Ti phase. This result provides a solid guide for the future design of high-strength titanium with the addition of Fe.

Study of natural aging on nanoparticles and their strengthening effect in Al-Mg-Si alloy

Atom probe tomography (APT) and transmission electron microscopy (TEM) were employed simultaneously to study nanoparticles and their strengthening effect in artificial aging (AA) Al-Mg-Si alloy with different natural aging (NA). We discovered that NA leads to formation of different type of nanoparticles meanwhile affect their fraction and dimension. Separation of the contribution from different types of nanoparticles to the alloy strength is conducted. In LNA-AA, β′ with a volume fraction of 0.16% contributions 54MPa to the yield strength while 0.14% β″ contributes 101MPa, which fully demonstrates that β″ is the main strengthening phase. The thermodynamic analysis was conducted for further research and the differential scanning calorimeter (DSC) results show that LNA forms more numerous clusters Ⅰ than SNA and consumes more vacancies and solute atoms then does not have enough driving force to precipitate clusters Ⅱ which are the nucleation sites of nanoparticles. When there is a certain distance between the nucleation sites, preferential growth of few β″ occur then converted to β′. The solute atoms in the region nearly which there is no nucleation site do not have enough driving force to diffuse and precipitate but stay in the matrix, reducing the volume fraction of the nanoparticles.

PRECIPITATION STATE OF WARM WORKED AA7050 ALLOY: EFFECT ON TOUGHNESS BEHAVIOR

Usually strength-toughness combination in aluminum alloys is improved by heat treatment (solid solution followed by quenching and reheating) after a deformation process at high temperature. In some cases a cold working step is added in the manufacturing process before heat treatment aimed to enhance the alloy strength. In recent time, some trials have been carried out finalized to replace the cold working step with a warm deformation. Such process route appeared to be quite effective in improving the toughness behavior of 7xxx alloys. Anyway e metallurgical explanation for such behavior has not still be reported . In this a comparison of the precipitation state following the two different routes is reported. Results show clear differences in the nanoprecipitation densities in the two cases, claiming for their responsibility in the definition of the toughness behavior.

Activities of Non-Basal Slips in Rolled Mg-Li and Mg-Ce Alloys Sheets

In this study, tensile tests of rolled Mg-Li alloy and Mg-Ce alloy sheets were carried out at room temperature to investigate effects of alloying additions on the relationship between mechanical properties and activities of slip systems in magnesium polycrystals. In Mg-Li alloy, ductility increased while strength decreased by lithium addition. Frequency of non-basal slips increased with increasing lithium content. In Mg-Ce alloy, strength and ductility were similar pure magnesium, and non-basal slips were hardly activated. Since critical resolved shear stress of non-basal slips were decreased by lithium addition, ductility of magnesium was increased while its strength was decreased.

Effect of Zn and Mg Content on Crashworthiness of Al-Zn-Mg Alloy Thin-Walled Square Extrusions

The effects of Zn and Mg content in thin-walled square extrusions of Al-Zn-Mg alloys on its crashworthiness were investigated, and the correlation between the crushing properties, mechanical properties, and microstructures of the profiles were investigated. The results showed that the strength and the compression properties were gradually increased with a decrease in the Zn/Mg ratios (from 12.48 to 4.57). When the Zn/Mg ratio is lower (less than 6.29), an increase in the Mg content simultaneously improves the alloy strength and the compression properties. An increase in Zn content (from 5.07 to 6.77) can improve the strength of the alloy however, it does not affect the compression properties. However, the higher Zn contents (6.77%) would lead to cracking in advance during the compressing, which reduces the compression energy absorption capacities of the product. Therefore, in order to obtain higher strength and excellent compression properties, the Zn/Mg ratio should be reduced. For the upper limit, the Zn content should not be too high (less than 6.77), as this may lead to early cracking and failure. For the lower limit, the Mg content should be higher (more than 0.91) to make sure that the alloy has excellent compression properties and higher strength.

Powder interlayer bonding of geometrically complex Ti-6Al-4V parts

Powder interlayer bonding (PIB) is a novel joining technique, which has been developed to facilitate high-integrity repairs of aerospace components, manufactured from commonly used titanium alloys. The PIB technique utilises an interlayer between complex geometric components which are mated under pressure and a highly localised heating source. In this study, induction heating enabled bonding in an inert fusion zone by use of an oxygen-displacing shielding gas, with particular attention to the initial heating and pressure application. These early stages proved crucial to the elimination of pores and consolidation of the alloy powder, with porosity volume fraction reduced to just 0.5% after just 20 sec at the bonding force. The technique has produced high-integrity bonds in alloys such as Ti-6Al-4V, retaining approximately 90% of the alloy strength in previous studies, offering advantages over established joining methods such as tungsten inert gas (TIG) and plasma arc (PA) welding due to a more highly localised heating and fusion zone. It is believed that powder interlayer bonding can compete against these techniques, providing a more time and cost-effective repair route for net shape components manufactured from a range of alloys with minimal post-processing.

Micro-Nanostructure Formation Mechanism of High-Mg Al Alloy

Micro-nanostructured materials have superior mechanical properties compared with coarse-grained materials. Severe plastic deformation (SPD) can effectively refine grains, resulting in the formation of typical micro-nanostructures. Fine grains improve alloy strength and toughness. This review summarizes the application of several typical SPD methods for high-Mg Al alloy. The effects of different SPD methods on the microstructure evolution, micro-nanostructure formation mechanism, and mechanical properties of the high-Mg Al alloy are analyzed in sequence. Finally, the development and future of the high-Mg Al alloy micro/nanostructure regulation are described.