Analysis of constitutive behaviours and processing map of 7020 aluminium alloy

Abstract

The authors present a study on the hot formability of 7020 aluminium alloy. Isothermal hot compression tests of solid cylindrical specimens were performed in the temperature range of 300–550°C and the strain rate range of 0·001–10 s–1. Stress–strain curves obtained from the experiment data are fitted using the Sellars–Tegart constitutive equation to obtain the constitutive parameters. Using the dynamic material model, the authors develop a processing map based on the flow stress data. The map shows that the parameters suitable for hot working are a temperature range of 450–550°C and a strain rate range of 0·001–0·1 s–1. This parameter range is where the efficiency of power dissipation is above 27% and where dynamic recrystallisation occurs. Unstable regions to be avoided in hot forming are deduced from an instability condition. The processing map is validated by comparing the microstructures of deformed compression specimens.

Tensile mechanical properties, constitutive parameters and fracture characteristics of an as-cast AA7050 alloy in the near-solidus temperature regime

“…Meanwhile, our alloy has a higher Q as compared to the homogenized AA7050, which have values between 160 and 170 kJ/mol for different homogenization routes [11,12]. As for the stress exponent (n), when compared to other 7XXX alloys, an AA7075 alloy has a stress exponent of 6.7 [5], while an as-cast AA7020 alloy -5.63 [50]. These results show that AA7XXX-series alloys demonstrate relatively higher stress exponents than other series of aluminum alloys.…”

“…However, the Q value of our alloy (185 kJ/mol) is within the range of other AA7XXX-series alloys. For example, an extruded AA7075 produces value around 131 kJ/mol [5], another work reports that aged AA7075 and AA7150 have values between 155 and 162 kJ/mol [48] and a solution treated AA7012 shows 200-230 kJ/mol [49], while an as-cast AA7020 is reported to have 173.8 kJ/mol [50]. When compared to other AA7050 alloys processed through different routes, our alloy has a lower Q as compared to the as-rolled AA7050 that produces 256 kJ/mol [13].…”

A Calculation Method of m Based on Processing Map

“…whereσ is the flow stress, MPa, ε is the strain rate, s-1 . According to Eq.1 and material flow behavior, the efficiency of power dissipation η can be deduced [4][5][6][7]. The η parameter describes the constitutive response of the work piece in terms of the various microstructural mechanisms that operate in a given regime of temperature and strain rate [8], and the value is as follows,…”

Comparative study of hot-processing maps for 6061 aluminium alloy constructed from power constitutive equation and hyperbolic sine constitutive equation

“…The hot-processing map, which can be divided into a safe domain and an unsafe domain, is a superimposition of a power-dissipation map and an instability map. This methodology has been used to optimise the hot workability of materials such as aluminium alloy, [5][6][7] magnesium alloy, [8][9][10] titanium alloy, 11 and others. [12][13][14][15][16] To avoid the complicated integral, the power constitutive equation s~K : e m is commonly used to represent flow behaviour of a material in constructing a hotprocessing map.…”

“…The hot-processing map, which can be divided into a safe domain and an unsafe domain, is a superimposition of a power–dissipation map and an instability map. This methodology has been used to optimise the hot workability of materials such as aluminium alloy, 5–7 magnesium alloy, 8–10 titanium alloy, 11 and others. 12–16…”