Take 4N9 high-purity aluminum, 4N9 refined magnesium ingot, Al-5Ti, al-3be, Al-12Si master alloy and ZL116 alloy ingot as raw materials, and carry out batching according to the composition in the table. 150 kg resistance crucible furnace with power of 75 kW is used for alloy melting. After melting, argon suspension blowing refining, skimming and standing, the temperature is adjusted to 720~730 ℃, and the gravity casting method is adopted for casting. The casting temperature is 720 ± 2 ℃, the casting time is 2 s, and the casting temperature is room temperature. The casting mold is a silica sol shell, and the shape of the casting is shown in the sample in the figure.
| Element | Mg | Si | Ti | Be | Al |
| Content | 0.45 | 7.5 | 0.2 | 0.3 | Bal. |
After casting, the chemical composition was analyzed by panalyticalaxios Max X-ray fluorescence spectrometer. T5 heat treatment for castings: solution treatment temperature is 535 ± 5 ℃, holding for 10 h, cooling method is water quenching, and water temperature is 50~60 ℃; Aging treatment temperature is 175 ± 5 ℃, holding for 6 hours, and cooling method is air cooling. After heat treatment, the casting was used after mechanical processing, anodizing and painting treatment. It was found that the casting arm was broken during use. Prepare metallographic samples from the position close to the fracture. The corrosive agent used is 1 ml hf+1.5 ml hno3+2.5 ml hcl+95 ml H2O.
Epihot300 optical microscope was used to observe the microstructure of metallographic samples. The fracture morphology was observed by Zeiss scanning electron microscope.