A study of the ageing behavior, microstructure, mechanical properties and stretch formability of an aluminum-copper-magnesium alloy (AA2024 aluminum alloy).

摘要

An Al-Cu-Mg alloy (AA2024 Al alloy) which is regarded as showing typical age hardening behaviour was aged at room temperature, 190{dollar}spcirc{dollar}C and 300{dollar}spcirc{dollar}C, respectively, to obtain three distinct types of ageing tempers. These tempers were identified as (1) 3 weeks at room temperature in the case of T4, (2) 9 hours at 190{dollar}spcirc{dollar}C in the case of T6 and (3) 20 hours at 300{dollar}spcirc{dollar}C in the case of T7.; A preliminary investigation of the influence of ageing time for these ageing temperatures was conducted in order to establish relative values, i.e., the basic mechanical properties and parameters.; A sheet material is usually processed into different shapes by forming operations. The material behaviour which governs the processing depends on its microstructure which changes during the processing. Therefore, for a better understanding of the correlation between microstructure and formability in the Al-Cu-Mg alloy, it is essential to determine the influence of each type of precipitate on the work hardening and the formability of the alloy. To achieve this, in this work, the microstructure evolution was observed by transmission electron microscopy (TEM). Examinations of the total configuration structures showed that the size and extent of the particular precipitate formed was a function of ageing time. High strength could, therefore, be obtained from a high volume fraction of particular configurations. Consequently, the size and distribution of the precipitates formed during ageing determined the relationship between strength and microstructure for this alloy.; In the final section of the present work, attention was given to a quantitative comparison of three different kinds of aged specimens (T4, T6 and T7, respectively) in terms of the influence of microstructural differences on mechanical properties and on the behaviour of these specimens in punch stretching. In this study the Forming Limit Curve (FLC) technique as described by Hecker was used. In this technique, a simulated cup was formed from the material and the cup height to fracture was measured during a punch-stretching test. This FLC test was conducted to assess the formability of this alloy under realistic forming conditions. The use of this technique combines all of the parameters and offers the best measure of stretchability.; The most important results of this study was that the naturally aged (T4) material which had an intermediate n value and higher m values yielded the greatest cup height to the fracture (formability). Even though their mechanical properties were different, the peak aged (T6) and the over-aged (T7) specimens were almost similar in formability behaviour. This study conclusively showed the inadequacy of the individual levels of mechanical parameters (such as n, m, uniform elongation, post-uniform elongation) to predict and explain the formability of an alloy in the Al-Cu-Mg alloy system. This study further indicates the necessity of knowing the complete structure factors such as size and distribution of second phase particles in order to be able to predict and explain the formability of this system with greater precision.