**1. Introduction**

40 Recent Trends in Processing and Degradation of Aluminium Alloys

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0924-0136

Light metals such as aluminum, magnesium, titanium and their alloys are useful for a wide range of applications such as in the automotive, railway, and aerospace industries. Engineering of fine-grained light metal materials is an indispensable technology that is expected to improve material properties such as tensile strength, elongation, corrosion resistance, fracture toughness, strain-rate plasticity, low-temperature plasticity, etc. The production of fine-grained light metals with excellent properties using severe plastic deformation methods, especially rolling and extrusion, has been intensively studied. With such processes, the size of the metal grain generally decreases because plastic deformation causes a decrease of grain size, by the principle shown schematically in Fig. 1.

Fig. 1. Schematic diagram of a) rolling method and b) extrusion method

On the other hand, the equal channel angular pressing (ECAP) method invented by Segal et al. in 1981 has proven successful for fabricating fine-grained bulk metals. A schematic diagram of the ECAP method is shown in Fig. 2. In the ECAP method, a large strain can be introduced into a billet sample by simple shear deformation without changes in the crosssectional area. In the ECAP process, the billet is extruded through a die consisting of two channels intersecting at an angle of 2Φ. The sample is set in the vertical channel and pressed into the second channel. The greatest advantage of the ECAP method is that the initial size

Rotary-Die Equal Channel Angular Pressing Method 43

obtained. One-pass RD-ECAP could be processed in 30 s. In this paper, the RD-ECAP process is explained and its use in the processing of light metals (aluminum alloys) is reported.

High pressure

Roll Up to 3 passes

Up to 3 passes?

2 or more passes

a)

b)

c)

Metallic material

Metallic material

Punch

Die

Punch

Metallic material

method in the case of two or more passes

Die

Fig. 3. Schematic diagram of a) rolling method and b, c) the equal channel angular pressing

and shape of the sample processed by the ECAP process are maintained. The sample is enhanced with the shear stress of the angle Φ to the extrusion direction in the ECAP process and its structure is fine-grained.

Fig. 2. Schematic diagram of equal channel angular pressing method. (V.M. Segal, V.I. Rexnikov, A.E. Drobysevsky and V.I. Kopylov: Metally Vol. 1 (1981), p. 115.)

The rolling method, the extrusion method and the ECAP method are severe plastic deformation methods, and are useful for grain refinement of light metals. In all of these methods, excellent grain refinement is generally expected with many passes. In the case of the rolling method, as shown in Fig. 3-a, the grain is continuously refined with each pass as the material's thickness decreases. In order to process the material with ECAP many times, either a continuous cycling method (Fig. 3-b) or a method of expulsion and reinsertion (Fig. 3-c) are possible. In the case shown in Fig. 3-b, twice or more pressure is necessary when continuing the second time, and there is a limit in the number of ECAP passes depending on the maximum pressure and the die strength. In conventional ECAP, as shown in Fig. 3-c, the pressed sample must be removed from the die and reinserted back for the next pressing, making the process inefficient. Not only does this process take a long time, the temperature of the sample is difficult to control.

A new ECAP process method called the rotary-die equal channel angular pressing (RD-ECAP) method was developed at Japan's National Institute of Advanced Industrial Science and Technology (AIST, formerly the National Industrial Research Institute of Nagoya (NIRIN)) to form fine-grained bulk materials such as aluminum alloys, aluminum composites, magnesium alloys, and titanium. Using the RD-ECAP method, ECAP processing of up to 2 passes can be done without sample removal, and samples processed over 30 cycles were

and shape of the sample processed by the ECAP process are maintained. The sample is enhanced with the shear stress of the angle Φ to the extrusion direction in the ECAP process

2Φ

Fig. 2. Schematic diagram of equal channel angular pressing method. (V.M. Segal, V.I.

The rolling method, the extrusion method and the ECAP method are severe plastic deformation methods, and are useful for grain refinement of light metals. In all of these methods, excellent grain refinement is generally expected with many passes. In the case of the rolling method, as shown in Fig. 3-a, the grain is continuously refined with each pass as the material's thickness decreases. In order to process the material with ECAP many times, either a continuous cycling method (Fig. 3-b) or a method of expulsion and reinsertion (Fig. 3-c) are possible. In the case shown in Fig. 3-b, twice or more pressure is necessary when continuing the second time, and there is a limit in the number of ECAP passes depending on the maximum pressure and the die strength. In conventional ECAP, as shown in Fig. 3-c, the pressed sample must be removed from the die and reinserted back for the next pressing, making the process inefficient. Not only does this process take a long time, the temperature

A new ECAP process method called the rotary-die equal channel angular pressing (RD-ECAP) method was developed at Japan's National Institute of Advanced Industrial Science and Technology (AIST, formerly the National Industrial Research Institute of Nagoya (NIRIN)) to form fine-grained bulk materials such as aluminum alloys, aluminum composites, magnesium alloys, and titanium. Using the RD-ECAP method, ECAP processing of up to 2 passes can be done without sample removal, and samples processed over 30 cycles were

Rexnikov, A.E. Drobysevsky and V.I. Kopylov: Metally Vol. 1 (1981), p. 115.)

Punch

Pressing

Die

Sample billet

and its structure is fine-grained.

ECAP processed sample billet

of the sample is difficult to control.

obtained. One-pass RD-ECAP could be processed in 30 s. In this paper, the RD-ECAP process is explained and its use in the processing of light metals (aluminum alloys) is reported.

Fig. 3. Schematic diagram of a) rolling method and b, c) the equal channel angular pressing method in the case of two or more passes

Rotary-Die Equal Channel Angular Pressing Method 45

Compared with the conventional ECAP die consisting of two channels intersecting at an angle, the RD-ECAP die is easy to make because the channels in the RD-ECAP die are formed with two straight holes. Though there are many channels in the RD-ECAP die, the sample is always pressed from the same direction and general press equipment can be used.

AC4C (JIS, ISO; Al-Si7Mg(Fe)) casting aluminum alloy (Cu<0.20, Si 6.5-7.5, Mg 0.20-0.4, Zn <0.3, Fe<0.5, Mn<0.6, Ni<0.05, Ti<0.20, Pb<0.20, Sn<0.05) is an excellent material for observation of the RD-ECAP effect, such as breaking of the precipitated phase, because the alloy has primary crystal dendrite and a coarse Al-Si microstructure. An AC4C casting aluminum alloy material 20 mm in diameter and 50 mm in length was used. Cylindrical

The RD-ECAP die had a two cylindrical holes 20 mm in diameter that intersect at 90° to form four channels. Three punches are pushed completely into the side and bottom channels, the sample is placed in the top hole, and the die is set onto a die holder, as shown in Fig. 4-a. Samples were processed under conditions of 543 K, 603K, 673 K at an

Photographs of AC4C aluminum alloy samples processed by the RD-ECAP are shown in Fig. 5. The surfaces of the samples were dirty with lubricants but had no cracks or

An experimentally obtained load-displacement curve of the plunger for the rotary-die equal channel angular pressing at 603 K is shown in Fig. 6. The load increased with pressing,

Change in the maximum stress with the number of rotary-die equal-channel angular pressing passes is shown in Fig. 7. The maximum load was lower at higher temperatures. At 673K, the first maximum load was about 150 MPa, and the fourth maximum load was about 100 MPa. At 603 K and 543 K, the maximum load decreased as RD-ECAP pass increased

Extruded direction

Fig. 5. Photograph of samples processed by rotary-die equal channel angular pressing

Before process

(2) 673 K

1 pass

2 passes

samples 19.5 mm in diameter and 40 mm in length long were prepared by lathing.

approximately 0.9 mm/s punch speed from one pass (= one extrusion) to 20 passes.

reached a maximum load, and then decreased with further sample deformation.

from the 1st to 6th pass. The decrease of the maximum load at 603 K was the highest.

**3. RD-ECAP processed aluminum** 

contamination after the RD-ECAP process.

(1) 523 K

Before process

1 pass

2 passes

**3.1 AC4C aluminum alloy** 
