Microstructure and Mechanical Properties of 7005 Aluminum Alloy Components Formed by Thixoforming

doi:10.1016/j.jmst.2016.07.014

摘要/Abstract

Abstract:

In the present research, semisolid billet of 7005 aluminum alloy was fabricated by using recrystallization and partial remelting (RAP), then thixoformed at different isothermal temperatures, preheating temperatures and load routes. Mechanical properties and microstructure of the thixoformed product were investigated. The results showed that microstructure achieved by three-step induction heating warm extruded 7005 aluminum alloy consists of a uniform and spheroidal microstructure suitable for thixoforming. Preheating temperature of the die affected significantly the filling status of semisolid billet of 7005 aluminum alloy. Complete filling status with good surface quality was obtained at a preheating temperature of 365 °C. Thixoformed microstructures consisting of relatively spheroidal grains illustrate the dependence of filling process on the sliding and rotating of solid grains rather than plastic deformation of solid grains. A non-uniform distribution of liquid phase was found in the different regions of the thixoformed product due to the slower adjustable velocity of solid grains as compared with liquid phase. Increase of isothermal temperatures led to a slight decrease of mechanical properties of the thixoformed product due to coarsening of solid grains. The highest yield strength, ultimate tensile strength and elongation of thixoformed components with T6 heat treatment are 237 MPa, 361 MPa and 16.8%, respectively, which were achieved at the isothermal temperature of 605 °C. Load route has a significant effect on mechanical properties and microstructure of the thixoformed product. Defects, such as crack and microporosity occurred in the microstructure of the thixoformed product obtained under load route 2. It led to an obvious reduction of mechanical properties as compared with route 1. A better compatibility of deformation caused by more liquid fraction at the isothermal temperature of 612 °C is beneficial to reducing non-uniformity of liquid phase in the different regions of the thixoformed product.

Key words: 7005 aluminum alloy, Microstructure, Mechanical properties, Semisolid billet, Thixoforming

. [J]. 材料科学与技术, 2017, 33(4): 379-388.

Jiang Jufu, Atkinson H.V., Wang Ying. Microstructure and Mechanical Properties of 7005 Aluminum Alloy Components Formed by Thixoforming[J]. J. Mater. Sci. Technol., 2017, 33(4): 379-388.

图/表 16

Fig. 1. Photographs of (a) thixoforming device, (b) sindanyo, (c) 7005 aluminum alloy, and (d) induction heating.

Fig. 2. Load routes carried out on the thixoforming of 7005 aluminum alloy.

Table 1 Process parameters determined in thixoforming of 7005 aluminum alloy

Experiment number	Preheating temperature of the die (°C)	Isothermal temperature of billet (°C)	Load route
1	365	605	Route 1
2	365	608	Route 1
3	365	610	Route 1
4	365	612	Route 1
5	300	605	Route 1
6	330	605	Route 1
7	365	612	Route 2

Fig. 3. Sampling regions of (a) induction heated sample and (b) thixoformed product.

Fig. 4. Microstructure of semisolid billet of 7005 aluminum alloy obtained by recrystallization and partial remelting in: (a) region of transverse specimen 1, (b) region of longitudinal specimen 1, (c) region of transverse specimen 2, (d) region of longitudinal specimen 2, (e) region of transverse specimen 3, and (f) region of longitudinal specimen 3.

Fig. 5. Photographs of filling status of the thixoformed product obtained at: (a) 300 °C, (b) 330 °C, and (c) 365 °C (isothermal temperature of 605 °C, load route 1).

Fig. 6. Microstructure of the thixoformed conduct at the isothermal temperature of 605 °C and die preheating temperature of 365 °C under load route 1 in: (a) region of transverse specimen 1, (b) region of longitudinal specimen 1, (c) region of transverse specimen 2, (d) region of longitudinal specimen 2, (e) region of transverse specimen 3, and (f) region of longitudinal specimen 3.

Fig. 7. Schematic diagram of filling process during the thixoforming of 7005 aluminum alloy at: (a) initial stage, (b) middle stage 1, (c) middle stage 2, and (d) final stage.

Fig. 8. Mechanical properties of the thixoformed product at different isothermal temperatures (die preheating temperature of 365 °C, load route 1).

Fig. 9. Microstructure evolution of the thixoformed product at isothermal temperatures: (a) 605 °C, (b) 608 °C, (c) 610 °C, and (d) 612 °C (die preheating temperature of 365 °C, load route 1).

Fig. 10. Comparison of mechanical properties from this work and other aluminum alloys.

Fig. 11. Mechanical properties of the thixoformed product under: (a) load route 1 and (b) load route 2 (isothermal temperature of 612 °C, die preheating temperature of 365 °C).

Fig. 12. X-ray radiographs of the thixoformed product obtained at isothermal temperature of 612 °C and die preheating temperature of 365 °C under load route 1 and load route 2: (a) front view of the thixoformed product 1 under load route 2, (b) right view of the thixoformed product 1 under load route 2, (c) front view of the thixoformed product 2 under load route 2, (d) right view of the thixoformed product 2 under load route 2, (e) front view of the thixoformed product 1 under load route 2, and (f) right view of the thixoformed product 4 under load route 1.

Fig. 13. SEM microstructures of the thixoformed product obtained at isothermal temperature of 612 °C and preheating temperature of 365 °C under load route 2: (a) thixoformed product 1 under load route 2, (b) thixoformed product 2 under load route 2.

Fig. 14. SEM microstructures of the thixoformed product 1 obtained at isothermal temperature of 612 °C and preheating temperature of 365 °C under load route 1: (a) region of transverse specimen 1, (b) region of longitudinal specimen 1, (c) region of transverse specimen 2, (d) region of longitudinal specimen 2, (e) region of transverse specimen 3 and (f) region of longitudinal specimen 3.

Fig. 15. Tensile fracture of the thixoformed product obtained at isothermal temperature of 612 °C and preheating temperature of 365 °C under load route 2: (a) thixoformed product 1 under load route 2, (b) thixoformed product 2 under load route 2 and (c) thixoformed product 1 under load route 1.

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