## 5 Research Progress on Key Technologies of IPPCS
### Material Upgrading of the Pressurized Capsule Structure  
#### 5.3.1 Application Analysis of Al-Mg-Sc Alloy in Pressurized Capsule Structure  
Figure 13 shows the optional aluminum alloy materials for the pressurized capsule structure in China. The 2219 aluminum alloy is a heat-treatment strengthening material. The size of the pressurized capsule structure is huge, and the heat treatment of the whole capsule cannot be carried out in China, which greatly reduces the allowable performance of structural materials. The 2195 aluminum alloy in China is not stable, and the supply specifications are limited. Therefore, it cannot be applied to the pressurized capsule structure at present. 5A06 aluminum alloy is the most mature weldable and corrosion-resistant aluminum alloy material used in China's pressurized capsule structure. Compared with 5A06 aluminum alloy, the yield strength and tensile strength of 5B70 aluminum alloy are increased by more than 70% and 20%, respectively, and the specific yield strength is significantly improved [45]. By comprehensive comparison, the performance characteristics of 5B70 are medium strength, weldable and corrosion-resistant. The comprehensive performance of 5B70 is excellent, which meets the material selection requirements of the pressurized cabin structure, and has great potential to replace 5A06 in the pressurized capsule structure. Figure 13: Typical aluminum alloy performance parameters for pressurized capsule structures [45]. 3.2 Analysis of Application Potential of Al-Mg-Sc Alloy in Deep Space Exploration Pressurized Capsule Structure  
The application potential analysis of 5B70 was carried out to meet the requirements of fatigue characteristics, fracture characteristics and large-scale material preparation of the pressurized capsule structure in deep space exploration. 1. Fatigue limit  
The change of fatigue characteristics was studied by comparing the high-cycle fatigue tests of 5B70 and 5A06. The high-cycle fatigue tests of the two materials were conducted under the same conditions, with both materials in the H32 state with a thickness of 6 mm. The test conditions were set at Kt = 1 and R = 0.1. Under a given life of N = 10\({}^{7}\) cycles, the median fatigue strength of 5B70 is \(\sigma_{50}\) = 272 MPa, while the median fatigue strength of 5A06 is \(\sigma_{50}\) = 160 MPa, as shown in Figure 14. The test data indicate that the fatigue limit of 5B70 has been significantly improved. The difference in fracture characteristics between 5B70 and 5A06 was studied through a comparison of fracture toughness tests. Both materials, 5B70 and 5A06, were in the H32 state with a thickness of 5 mm. The specimen orientations included along the L direction (rolling direction) and along the T direction (perpendicular to the rolling direction). The fracture toughness test results for both L and T directions are presented in Table 2. In both directions, the fracture toughness of 5B70 was found to be superior to that of 5A06, indicating that 5B70 material has better fracture resistance. 3. Large size and ultra-large thickness plate supply  
With breakthroughs in key technological processes such as the stabilized control technology for ultra-thick plates, China has acquired the capability to mass-produce large-size, ultra-thick plates of 5B70 with widths exceeding 3500 mm and thicknesses exceeding 50 mm. As the engineering application of 5B70 material is being promoted, the usage of 5B70 material is gradually increasing and surpassing the minimum supply threshold. The increased usage beyond the threshold helps to ensure continuous production and stable quality of the raw materials and can significantly reduce the raw material prices. \begin{table}
\begin{tabular}{c c c} \hline
**Preset Crack Orientation** & **5A06 KR(MPa-m\({}^{1/2}\))** & **5B70 KR(MPa-m\({}^{1/2}\))** \\ \hline Direction L & 105.6 & 115.018 \\ Direction T & 110.2 & 120.237 \\ \hline \end{tabular}
\end{table} 
Table 2: Fracture toughness of 5A06 and 5B70. Figure 14: High cycle fatigue properties of 5B70 and 5A06.