Effect of Sc on the Hot Cracking Properties of 7xxx Aluminum Alloy and the Microstructure of Squeeze Castings

In this paper, the effect of adding the refiner Sc to the high Zn/Mg ratio 7xxx series aluminum alloy melt on the hot tearing performance, microstructure, and mechanical properties of the alloy is studied. The hot tearing performance test (CRC) method is used to evaluate the hot tearing performance of the alloy. The squeeze casting process was used to form solid cylindrical parts to analyze the structure and properties of the alloy. This study shows that the hot cracking sensitivity of the alloy after the addition of the refiner Sc is significantly reduced. The ingot grain size is significantly reduced, and the average grain size is reduced from about 86 μm to about 53 μm. While the mechanical properties are significantly improved, and the tensile strength reduced from 552 MPa is increased to 571 MPa, and the elongation rate is increased from 11% to 14%.

Review On Progress of 7xxx Series Aluminum Alloy Materials

Since the first generation of 7xxx superhard aluminum alloy was investigated in 1930, hitherto the fifth generation aluminum alloy materials with high comprehensive properties such as high static strength, high strength, heat resistance, high toughness, damage resistance, low density and low quenching sensitivity have been improved and developed. This paper reviews the progress of 7xxx aluminum alloy materials in composition, microstructure, properties, preparation methods, heat treatment strengthening and applications from 2014 to 2021. The effect of adding trace elements on microstructure and properties of 7xxx series alloy and the problems existing in aging precipitation characteristics and reinforcement mechanism are discussed. The future development direction of 7xxx superhard aluminum alloy is prospected by optimizing heat treatment technological, adding appropriate trace elements to alloy and controlling alloy microstructure.

Mechanism of Fracture in Pre-Cracked Single-Edged Notched Bars With AI2O3-TiO2 and WC-CO Coatings

Experimental analysis is made to investigate the most significant fracture characterizing parameters in plasma sprayed substrate-coating composite. The experiments were conducted on the single edge notched bars (SENB) made with 7075 series aluminum alloy, with plasma sprayed Al2O3-TiO2 and WC-Co top coats. The pre-cracked bars were fractured in computerized universal testing machine in controlled conditions. The material has been tested under age-hardened and coated conditions also. The results have revealed that the age hardening and type of coating have a much influence on strain energy release rate. The experimental results have shown that WC-Co coated normal materials possess higher strength whereas uncoated normal materials possess lower strength. It is also found that Al2O3-TiO2 coated material possess better coating bond strength and moderate load bearing capacity. The SEM fractographic analysis has been made to analyze the fracture behavior as a function of coating type and the material conditions.

Examination of Sensitization on 5xxx Series Aluminum Alloy Sheets from Structural Parts of Hellenic Navy High-Speed Craft

Al - Mg alloys are extensively used as structural materials in marine applications. Sensitization has emerged as a severe concern during the operation of aluminum vessels, due to the consequent high susceptibility to Intergranular Corrosion - IGC. Herein, a detailed study of sensitization on naturally sensitized, field retrieved, Al-Mg alloy samples, is presented. Specifically, samples from four Hellenic Navy - HN high speed vessels were tested according to ASTM G67 in order to quantify their Degree of Sensitization - DoS and qualified, in terms of grain boundaries (GBs) coverage with β phase with microstructural observation using Scanning Electron Microscopy - SEM and light optical microscopy. Consequently, the correlation of DoS value to the external factors that affect it becomes possible. Remarkably, material under investigation has significantly diverse chemical composition, compared to common marine grade aluminum alloys. Ultimately, correlation of Stress Corrosion Cracking behavior with the microstructure is discussed.