Improvement in Thixoforging of 7075 Aluminium Alloys at High Solid Fraction

Abstract

Abstract. Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5<f s <1). 7075 aluminium alloys have been used as a feedstock for thixoforging in order to investigate thixoformability of a high performance aluminium alloy at high solid fraction. Higher solid fraction of 7075 alloy is less sensitive to temperature, avoids metal splash at high speed and allows laminar flow at high speed. Hot tool combined with lubricant tool coating are used to slow down the solidification rate of the high solid fraction metal by decreasing thermal exchanges with the tool. Improved thermal and forming parameters [1-2] will be applied to produce an automotive component by thixoforging and mechanical properties have been measured from tensile samples. High mechanical properties are obtained after T6 thermal treatment.

Influence of Parameters during Induction Heating Cycle of 7075 Aluminium Alloys with RAP Process

“…But some non recrystallized grains remain for short cycle on the axis of the slug due to the low energy stored in the axis during extrusion. We will observe influence of these elongated grains on thixoforged parts [6].…”

“…There are no major impacts on the microstructure (grain size, shape or solid fraction). A few unrecrystallised grain remain but their resistance to the material flow during thixoforging should be minor due to their low thickness [6]. A seven step heating cycle is used to approach slowly, in a homogeneous way, a target temperature whilst allowing kinetic transformations like the solid-liquid transition to occur.…”

Electron backscattered diffraction of aluminium alloy 7075 samples after heat treatment

“…the migration of the high angle boundary) to occur [2,5]. Thixoforming involves forming alloys in the semisolid state to near net shaped products [6][7][8]. The required spheroidal microstructure can be obtained by a number of routes, including the Strain Induced Melt Activated method (SIMA) [9] and Recystallisation And Partial melting (RAP) [10].…”

Thermal Profiles and Fraction Solid of Aluminium 7075 at Different Cooling Rate Conditions

“…Vaneetveld et al found that superior mechanical properties resulted from the use of a higher tool temperature setting and appropriate tool punch speed during thixoforming [10]. These settings so adjusted resulted in reduced cracking which was noted to occur due to overly fast cooling rates.…”

“…Aluminium 7075 has recently been investigated for use in the of semi-solid metal (SSM) processing [7][8][9][10][11][12]. The performance of aluminium 7075 was investigated using both thixoformed cooling slope and recrystallization and partial melting (RAP) route in order to compare their mechanical properties [7].…”