Development of Precipitation Hardening Parameters for High Strength Alloy AA 7068

Abstract

The mechanical properties after age hardening heat treatment and the kinetics of related phase transformations of high strength AlZnMgCu alloy AA 7068 were investigated. The experimental work includes differential scanning calorimetry (DSC), differential fast scanning calorimetry (DFSC), sophisticated differential dilatometry (DIL), scanning electron microscopy (SEM), as well as hardness and tensile tests. For the kinetic analysis of quench induced precipitation by dilatometry new metrological methods and evaluation procedures were established. Using DSC, dissolution behaviour during heating to solution annealing temperature was investigated. These experiments allowed for identification of the appropriate temperature and duration for the solution heat treatment. Continuous cooling experiments in DSC, DFSC, and DIL determined the kinetics of quench induced precipitation. DSC and DIL revealed several overlapping precipitation reactions. The critical cooling rate for a complete supersaturation of the solid solution has been identified to be 600 to 800 K/s. At slightly subcritical cooling rates quench induced precipitation results in a direct hardening effect resulting in a technological critical cooling rate of about 100 K/s, i.e., the hardness after ageing reaches a saturation level for cooling rates faster than 100 K/s. Maximum yield strength of above 600 MPa and tensile strength of up to 650 MPa were attained.

Comprehensive Study for Impure and Pure Casts of Aluminum and Copper

“…The established samples are divided into two main groups (impure and pure). The impure group consists of 7 samples for various Al and Cu percentages of weights (1) . On the other hand, the pure group consists of 6 samples for various Al and Cu percentages of weights too.…”

“…Tables 3 and 4 show the details and measurements of the Al-Cu cast alloys for both impure and pure groups, respectively. (1) Weight Percentage (wt%) can be converted to Atomic weight Percentage (At%). First of all, the measured HV, HB and TS values for the impure cast alloys are more fluctuated than the pure cast alloys.…”

“…The resulted cast alloy has different specifications that are completely different from essential characteristics of each component element. The cast alloys can be made by a combination between two or more elements of Aluminium (Al), Copper (Cu), Zinc (Zn), Magnesium (Mg), Manganese (Mn), Silicon (Si) and others [1]. Fig.…”

“…That is, their cast alloys may have significant mechanical properties such as hardness and high strength, and good machinability [7]. They are used in some important manufacturer such as bus bodies, beverage cans and automotive parts [1]. Al-Cu chain alloys can be utilized for the machine parts, aircraft materials and structural materials.…”

Effect of Multistage Solution Aging Heat Treatment on Mechanical Properties and Precipitated Phase Characteristics of High-Strength Toughened 7055 Alloy

“…Al-Zn-Mg-Cu series (7XXX series) aluminum alloys find extensive application in the modern military, automotive transportation, and aerospace sectors for heavy structural components, owing to their exceptional properties, such as low density, ultra-high strength, high fracture toughness, excellent fatigue resistance, and stress corrosion resistance [1][2][3][4][5][6][7][8][9]. Since the beginning of the 21st century, spurred by the rapid advancements in the aerospace industry, the utilization rate of high-strength, high-toughness aluminum alloys in aircraft structure manufacturing has surpassed 90%.…”