FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF INVENTION
A method of heat treatment of an aluminium alloy; and a rotor assembly
thereof
APPLICANT(S)
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR (S)
Mudragada Sathyanarayana, Chinmalli Onkar Mallikarjun, Shaikh Bashit and Dumbre Jayshri; all of Crompton Greaves Ltd., Advanced Materials and Process Technology Center, CG Global R&D Centre, Kanjur Marg (E), Mumbai - 400042, Maharashtra, India; and Alakkal Kizhakkethil Sivadas of Crompton Greaves Ltd., Advanced Motor Design and Technology Center, CG Global R&D Centre, Kanjur Marg (E), Mumbai - 400042, Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION:
This invention relates to the field of metallurgy and metal treatment.
Particularly, this invention relates to treatment of aluminium alloy.
Specifically, this invention relates to a method of heat treatment of an aluminium alloy and a rotor assembly, thereof.
BACKGROUND OF THE INVENTION:
Motors are machines that convert electrical energy to mechanical energy. The main components of a motor are stator and rotor. The rotor is a rotating part of the motor while the stator is a stationary part of the motor. Stampings are used in the manufacture of stators as well as rotors for motors and /or other electrical or rotary machine equipment.
'Aluminium alloy (LMO, LM6 or A413.1 and LM 24) grades are used as rotor bars to make squirrel cage rotors by pressure die casting method. One application of such rotors is in fans.
Pressure die casting process is basically one of the fastest casting techniques and accepted worldwide on a larger scale. Around 50% of light weight metals like aluminium, zinc, magnesium are cast using this technique for various applications.
Another very important factor for using this technique is that castings have complicated shapes e.g. rotors in induction motors and fans can be easily cast by this method as cavities can be easily filled due to pressure applied for filling them. One of the more undesirable effects of this method is presence of porosity in larger

amount when compared to other casting methods due to high velocity of plunger in order to fill the casting cavity. This porosity drastically affects the electrical conductivity of the casted component. Another important factor for resistivity of aluminium alloy (LM6) alloy is its structure (dendritic structures and morphology of silicon) and elements (Si, Fe, Mg, Mn, and the like) are in solid solution.
Generally, LM6 is not heat treatable for improvement of mechanical properties.
Table 1, below depicts a typical composition of aluminium alloy of LM6 grade.
Table 1. Composition of aluminium alloy LM6 grade

Alloy Composition mass %

Si Fe Cu Mn Mg Ni Zn Al
A413.0 (LM6) 11.0-13.0 1.3 max 1.0 max 0.35 max 0.1 max 0.05 max 0.15 Max Rem
Table 1
Also, according to the prior art, there is direct use of as-cast aluminium alloy (LM 6) rotors in fans without any treatment.
There is a need for treatment of the material used for casting of rotors for their improved operation and performance. There is scope of improvement of parameters relating to increase in electrical conductivity of rotor bars resulting into reduction of rotor losses and hence, increase in rpm of rotor, and decrease in power consumption of the motor.
Figure 1 illustrates a typical process work flow for rotor manufacturing and fan assembly.

PRIOR ART:
IN228447 discloses processing techniques in order to produce microstructures which optimize the physical, mechanical and thermal properties of the constituent phases of the composite.
US20120217060 discloses a method for manufacturing an aluminum alloy wire where heating is done and controlled cooling is done.
However, there is a need for an alloy, particularly an aluminium alloy, and specifically, an aluminium alloy of LM6 grade which provides improved characteristics in terms of improved conductivity and improved performance of products made out of the improved aluminium alloy of LM6 grade. There is also a need for a method which provides the improved aluminium alloy of LM6 grade, which method is an improved method.
OBJECTS OF THE INVENTION:
An object of the invention is to provide a heat treatment method and process for rotors for use in induction principle motors.
Another object of the invention is to provide a heat treatment method and process for rotors for use in induction principle motors, which rotors are cast of aluminum alloy.
Yet another object of the invention is to a heat treatment method and process for rotors for use in induction principle motors, which rotors are cast of aluminum alloy 6f LM6 grade.

Still another object of the invention is to provide a heat treatment method and process for rotors for use in induction principle motors, which rotors are cast of aluminum alloy and which rotors have improved electrical conductivity.
An additional object of the invention is to provide a heat treatment method and process for rotors for use in induction principle motors, which rotors are cast of aluminum alloy and which rotors have higher performance rating.
Yet an additional object of the invention is to provide a heat treatment method and process for rotors for use in induction principle motors, which rotors are cast of aluminum alloy and which rotors have higher performance rating in terms of rpm. Still an additional object of the invention is to provide a heat treatment method and process for rotors for use in motors, which rotors .are cast of aluminum alloy arid which rotors have higher performance rating in terms of relatively lower wattage.
Another additional object of the invention is to provide a heat treatment method and process for rotors for use in induction principle motors, which rotors are cast of aluminum alloy and which rotors have higher performance rating in terms of relatively higher efficiency.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a method of heat treatment of an
aluminium alloy, said method comprises the steps of:
k. heating said aluminium alloy in a furnace up to a first pre-determined
temperature; b. soaking said heated aluminium alloy at a first pre-determined temperature for
a pre-determined duration of time; and

c. cooling said soaked aluminium alloy by switching off said furnace or by controlled cooling in said furnace or by water quenching to ambient temperature after said pre-determined time.
According to this invention, there is also provided a method of preparing rotor assembly made of an aluminium alloy, said method comprising the steps of: I. heating said aluminium alloy in a furnace up to a first pre-determined
temperature; II. soaking said heated aluminium alloy at a first pre-determined temperature for a pre-determined duration of time;
III. cooling said soaked aluminium alloy by switching off said furnace or by
controlled cooling in furnace or by water quenching to ambient temperature
after said pre-determined time; and
IV. using said treated aluminium alloy to obtain said rotor assembly.
According to this invention, there is provided a method of heat treatment of an aluminium alloy, said method comprises the steps of:
i. heating said aluminium alloy in a furnace up to a first pre-determined
temperature; ii. soaking said heated aluminium alloy at a first pre-determined temperature for
a pre-determined duration of time; iii. cooling said soaked aluminium alloy by switching off said furnace or by
controlled cooling in said furnace after said pre-determined time up to a
second pre-determined temperature; and iv. water quenching or furnace cooling or air cooling said furnace cooled
aluminium alloy for cooling from said second pre-determined temperature to
ambient temperature.

According to this invention, there is also provided a method of preparing rotor assembly made of an aluminium alloy, said method comprising the steps of:
A. heating said aluminium alloy in a furnace up to a first pre-determined
temperature;
B. soaking said heated aluminium alloy at a first pre-determined temperature for
a pre-determined duration of time;
C. cooling said soaked aluminium alloy by switching off said furnace or by
controlled cooling in said furnace after said pre-determined time up to a
second pre-determined temperature;
D. water quenching or furnace cooling or air cooling said furnace cooled
aluminium alloy for cooling from said second pre-determined temperature to
ambient temperature; and
E. using said treated aluminium alloy to obtain said rotor assembly.
Typically, said aluminium alloy is an LM6 grade aluminium alloy.
Typically, said first pre-determined temperature is between 200°C and 525°C.
Preferably, said first pre-determined temperature is 420°C.
Alternatively, said first pre-determined temperature is 450°C.
Typically, heating rate is 1 to 10 °C / minute.
Typically, said pre-determined time is between 5 minutes to 180 minutes.
Preferably, said pre-determined time is 60 minutes.

Typically, said second pre-determined temperature is 150 to 250°C.
Typically, said rotor is an aluminium alloy die cast rotor.
Preferably, said rotor is an aluminium alloy (LM6 grade) die cast rotor.
According to this invention, there is also provided a rotor assembly made from the said treated aluminium alloy.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates a typical process work flow for rotor manufacturing and fan assembly.
The invention will now be described in relation to the accompanying drawings, in which:
Figure 2 illustrates a heat treatment cycle for Sample no. 3 (420°C for 1 hr and furnace cooling up to200°C followed by water quenching);
Figure 3 is a graphical representation of conductivity (%IACS) and for as cast and heat treated samples;
Figure 4 illustrates micro samples of end rings which were showing the porosity in the as cast sample: a) top end ring; and b) bottom end ring;
Figure 5 illustrates the small blisters were observed after 420 °C heat treatment;

Figure 6 illustrates the heat treated samples at 420°C for 1 hr soaking time - a) water quenching and b) furnace cooling up to 200°C followed by water quenching; and
Figure 7 illustrates the heat treated at 450°C for 1 hr soaking time - a) water quenching and b) furnace cooling up to 200°C followed by water quenching; and
Figure 8 illustrates a flowchart of the steps involved in the method of a rotor of
I •" ■.
aluminium alloy (LM6 grade).
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided a method of heat treatment of a rotor, and a rotor assembly, thereof. Particularly, the rotor is an aluminium alloy die cast rotor. Specifically, the rotor is an aluminium alloy - LM6 grade die cast rotor.
Figure 8 illustrates a flowchart of the steps involved in the method of a rotor of aluminium alloy (LM6 grade).
The basic principle for electrical conductivity in metals is the flow of electrons and the basic aim of this invention is to enhance the electrical conductivity of the aluminium alloy (LM 6) in the rotor castings.
In accordance with an embodiment of this invention, the rotor bars are heat treated to a first pre-determined temperature with an optimum pre-defined soaking time and cooled in a pre-defmed cooling rate up to a second pre-determined temperature and finally to ambient temperature. But, according to the prior art, these alloys (LM 6) are not heat treatable in terms of mechanical properties. Therefore, structural changes occur and elements that are out of solution influence the reduction in

electron scattering and improve flow of electrons in the alloy, thereby improving conductivity and related / associated parameters.
In accordance with an embodiment of this invention, the aluminium alloy (LM6 grade) is heated in a furnace up to a first pre-determined temperature. The range of this first pre-determined temperature is between 200°C and 525°C. Optimum temperature to be achieved while heating is 420°C. Typically, heating rate is about
5°C / minute and it can vary from 1 to 10°C / minute. This is Step I.
c... In accordance with another embodiment of this invention, the heated aluminium alloy (LM6 grade) is soaked at the first pre-determined temperature for a predetermined duration of time. The range of this time is between 5 minutes to 180 minutes. Optimum time is 60 minutes. This is Step II.
In accordance with yet another embodiment of this invention, the soaked aluminium alloy (LM6 grade) is allowed to be cooled by switching off the furnace or controlled cooling in the furnace or by water quenching to ambient temperature after the predetermined time. This is Step III.
Alternatively, natural cooling gradient may last up to 180 minutes by which time, the aluminium alloy (LM6 grade) reaches to about a second pre-determined temperature. This second pre-determined temperature is 150 to 250°C. This process is furnace cooling. This is alternate to Step III.
In accordance with still another embodiment of this invention, the furnace cooled aluminium alloy (LM6 grade) is water quenched or furnace cooled or air cooled for relative rapid cooling from the second pre-determined temperature to ambient

temperature. This process of furnace cooling followed by relative rapid cooling results in minimal thermal stresses, these stresses does not affect electrical properties, thereby resulting in a better heat treated aluminum alloy (LM6 grade). This is Step IV.
The invention will now be explained in accordance with non-limiting exemplary embodiments, as discussed below.
For performing heat treatment experiments, according to a non-limiting exemplary embodiment, a fan rotor was cut into four similar sections (Sample no. 1, 2, 3, and 4) (as seen in Figure 3 of the accompanying drawings) so that each sample would undergo different heat treatment cycles. Two samples (1 and 3) were heat treated at 420°C for 1 hr and other two samples (2 and 4) were heat treated at 450°C for 1 hr. After soaking for 1 hr, at both the temperatures, one (1 and 2) out of the two samples was water quenched and the other (3 and 4) was furnace cooled up to 200°C followed by water quenching. A complete heat treatment cycle for Sample no. 3 is graphed in Figure 2 of the accompanying drawings.
Conductivity of aluminum was measured for all samples before and after performing
the heat treatment experiments by using a two probe (eddy current principle)
method. Similarly, microstructure analysis was done for heat treated samples.
The Table 2, given below, shows the conductivity values recorded for as cast as well as for sample nos. 1, 2, 3 and 4, which had undergone different heat treatment cycles. A graphical representation of these results is made in Figure 3. It is clearly seen that there is an increase in conductivity values after heat treatment. Improvement of around 30% (from 29.53%IACS to 38.67%IACS) was recorded for

sample no. 4 which was heat treated at 450°C soaked for 1 hr, furnace cooled till 200°C followed by water quenching. Whereas improvement of around 25.5% (from 29.67%IACS to 37.23%IACS) was recorded for sample no. 3 which was heat treated at 420°C soaked for 1 hr and furnace cooled till 200°C followed by water quenching. The other two samples which were directly water quenched did show improvement in conductivity but was less than that of above mentioned samples.
Table 2 shows Conductivity (% IACS) of as cast and heat treated samples (Two probe method).

Part description -aluminum cast
t - Bottom
end Ring L Bottom
end Ring T Top End Ring L Top
End
Ring T Top
As-cast 30.64 25.91 32.6 27.69 28.45

31.31 27 32.42 27.19 28.57

30.95 27.77 32.55 26.64 28.31

30.61 25.99 32.37 26.51 28.28

30.76 25.63 32.38 27.56 28.02

30.69 36.91 32.08 27.59 27.45

31.45 26.18 32.56 27.23 27.69

30.37 26.47 32.16 27 28.13

Avg. 30.85 27.73 32.39 27.18 28.11

Avg. 29. 29 29. 78 28.11
HT 420 °C
@ 60 min. W/Q
(sample 1) 36.9 30.96 36.92 32.84 36.93

37.33 31.44 36.87 32.53 37.1

36.74 32.15 36.97 32.48 36.83

36.79 30.78 37.06 32.16 36.82

37.12 30.94 37.1 31.5 37.02

37.06 31.47 36.99 31.59 36.41

36.9 30.87 37.04 32.28 36.77

Avg. 36.98 31.23 36.99 32.20 36.84

Avg. 34. 10 34. 60 36.84

HT 420 °C 39.48 35.07 39.6 35.55 38.94
@60min.F/C 39.49 33.93 39.64 35.48 39.08
(sample 3) 39.17 34.8 39.66 34.32 38.86
39.55 35.02 39.52 35.05 39.09
39.73 35.33 39.57 33.61 38.87
39.77 34.51 39.56 35.65 38.8
39.14 34.74 39.92 35.67 39.59
Avg. 39.48 34.77 39.64 35.05 39.03
Avg. 37.12 37.34 39.03
HT 450 °C 37.23 33.64 37.12 34.43 36.9
@ 60 min. W/Q 37.09 34.5 37.21 32.62 36.97
(sample 2) 37.04 34.31 37.32 34.61 36.75
36.75 34.28 37.06 34.21 36.96
37.13 32.13 37.25 34.65 36.9
37.04 32.67 37.37 34.56 36.63

37.32 32.87 37.32 34.51 37.28

Avg. 37.09 33.49 37.24 34.23 36.91

Avg. 35. 29 35.73 36.91
HT450°C
@60min.F/C
(sample 4) 40.39 36.68 39.46 37.62 39.6

40.01 37.89 39.52 37.62 39.29

39.62 37.51 39.88 38.17 39.76
40.25 36.85 39.79 37.98 40.41
39.84 37.83 40.03 37.01 39.17
40.18 37.97 39.82 36.21 40.34
Avg. 40.05 37.46 39.75 37.44 39.76
Avg. 38. 75 38.59 39.76
Table 2 (where L: longitudinal and T: transverse cross section)
Figures 4a and 4b illustrate the porosity in the samples observed after polishing under stereo microscope.
Figure 5 illustrates the small blisters that were observed after 420 °C heat treatment.

Figure 6 illustrates the heat treated samples at 420°C for 1 hr soaking time: a) water quenching; and b) furnace cooling up to 200°C followed by water quenching -showing the uneven distribution (segregation) of silicon particles in the aluminium matrix. Figure 6a shows that there are flaky (not spherical) structures of silicon particles where as Figure 6b shows the near to spherical silicon particles are observed in the aluminium matrix.
Figure 7 illustrates the heat treated sampled at 450°C for 1 hr soaking time: a) water quenching; and b) furnace quenching up to 200°C followed by water quenching -Figure 7a shows equal distribution of the silicon particles in aluminium matrix but are flaky (not spherical) structure where as Figure 7b shows equal distribution of silicon particles in the aluminium matrix and these particles are near spherical in shape. After above trials, the 420 °C heat treatment was selected, for four numbers of fan rotors.
Table 3 shows results for fan testing at 230V with existing stator (Line 0, Line 1 & Line 2 are rotors from existing process where as HT 1 is treated at 400 °C @ 60 min soaking followed by furnace cooling up to 200 °C and then water quenched; and HT 2, HT 3, HT4 & HT 5 are treated at 420 °C @ 60 min soaking followed by furnace cooling up to 200 °C and then water quenched).

Sample No. Motor current
(Amps) Motor input
Power
(Watts) Speed (RPM)
Line 0 0.325 74.2 373
Line 1 0.325 74.1 380
Line 2 0.323 73.4 371
HT1 0.335 76.7 381
HT2 0.332 76.1 396
HT3 0.333 76.1 395
HT4 0.336 76.1 392
HT5 0.334 75.9 394
Table 3
The Technical Advancement of this invention lies in providing a heat treatment method for an aluminium alloy, preferably of LM6 grade which is used for rotor construction. This heat treatment method provides an improved aluminium alloy and rotor, therefore wherein:
1) it results in electrical conductivity improvement due to microstmctural changes occurred (change in cast structure and change in morphology of silicon);
2) it results in electrical conductivity improvement up to 25% on aluminium rotor die cast samples used in fans;
3) it results in reduction of rotor losses;
4) it results in increase in motor efficiency; and
5) it results in reduction in power consumption and increase in speed.

The principle of improvement of electrical conductivity for aluminium-silicon (LM 6) alloys is mainly based on reduction of electron scattering due to cast structural changes.
While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim,
1. A method of heat treatment of an aluminium alloy, said method comprising the steps of:
a. heating said aluminium alloy in a furnace up to a first pre-determined
temperature;
b. soaking said heated aluminium alloy at a first pre-determined
temperature for a pre-determined duration of time; and
c. cooling said soaked aluminium alloy by switching off said rurnace or
by controlled cooling in said furnace or by water quenching to ambient
temperature after said pre-determined time.
2. The claim as claimed in claim 1, wherein said aluminium alloy is an LM6 grade aluminium alloy.
3. The claim as claimed in claim J, wherein said first pre-determined temperature is between 200°C and 525°C.
4. The claim as claimed in claim 1, wherein said first pre-determined
temperature is 420°C.
5. The claim as claimed in claim 1, wherein said first pre-determined temperature is 450°C.
6. The claim as claimed in claim 1, wherein heating rate is 1 to 10 °C / minute.
7. The claim as claimed in claim 1, wherein said pre-determined time is between 5 to 180 minutes.

8. The claim as claimed in claim 1, said pre-determmed time is 60 minutes.
9. A method of preparing rotor assembly made of an aluminium alloy, said method comprising the steps of:
I. heating said aluminium alloy in a furnace up to a first pre-determined
temperature; II. soaking said heated aluminium alloy at a first pre-determined temperature for a pre-determined duration of time;
III. cooling said soaked aluminium alloy by switching off said furnace or by controlled cooling in furnace or by water quenching to ambient temperature after said pre-determined time; and
IV. using said treated aluminium alloy to obtain said rotor assembly.
10. The claim as claimed in claim 9, wherein said aluminium alloy is an LM6
grade aluminium alloy.
11. The claim as claimed in claim 9, wherein said first pre-determined temperature is between 200°C and 525°C.
12. The claim as claimed in claim 9, wherein said first pre-determined temperature
is 420°C.
13. The claim as claimed in claim 9, wherein said first pre-determined temperature is450°C.
14. The claim as claimed in claim 9, wherein heating rate is about 1 to 10°C /
minute.

15. The claim as claimed in claim 9, wherein said pre-determined time is between 5 to 180 minutes.
16. The claim as claimed in claim 9, wherein said pre-determined time is 60 minutes.
17. The claim as claimed in claim 9. wherein said rotor is an aluminium alloy die cast rotor.
18. The claim as claimed in claim 9, wherein said rotor is an aluminium alloy (LM6 grade) die cast rotor.
19. A method of heat treatment of an aluminium alloy, said method comprising
the steps of:
i. heating said aluminium alloy in a furnace up to a first pre-determined
temperature; ii. soaking said heated aluminium alloy at a first pre-determined
temperature for a pre-determined duration of time; iii. cooling said soaked aluminium alloy by switching off said furnace or
by controlled cooling in said furnace after said pre-determined time up
to a second pre-determined temperature; and iv. water quenching or furnace cooling or air cooling said furnace cooled
aluminium alloy for cooling from said second pre-determined
temperature to ambient temperature.
20. The claim as claimed in claim 19, wherein said aluminium alloy is an LM6
grade aluminium alloy.

21. The claim as claimed in claim 19, wherein said first pre-determined temperature is between 200°C and 525°C.
22. The claim as claimed in claim 19, wherein said first pre-determined
temperature is 420°C.
23. The claim as claimed in claim 19, wherein said first pre-determined temperature is 450°C.
24. The claim as claimed in claim 19, wherein heating rate is from 1 to 10 °C / minute.
25. The claim as claimed in claim 19, wherein said pre-determined time is between 5 to 180 minutes.
26. The claim as claimed in claim 19, said pre-determined time is 60 minutes.
27. The claim as claimed in claim 19, said second pre-determined temperature is
150 to 250°C.
28. A method of preparing rotor assembly made of an aluminium alloy, said method comprising the steps of:
A. heating said aluminium alloy in a furnace up to a first pre-determined
temperature;
B. soaking said heated aluminium alloy at a first pre-determined
temperature for a pre-determined duration of time;

C. cooling said soaked aluminium alloy by switching off said furnace or
by controlled cooling in said furnace after said pre-determined time up
to a second pre-determined temperature;
D. water quenching or furnace cooling or air cooling said furnace cooled
aluminium alloy for cooling from said second pre-determined
temperature to ambient temperature; and
E. using said treated aluminium alloy to obtain said rotor assembly.
29. The claim as claimed in claim 28, wherein said aluminium alloy is an LM6 grade aluminium alloy.
30. The claim as claimed in claim 28, wherein said first pre-determined temperature is between 200°C and 525°C.
31. The claim as claimed in claim 28, wherein said first pre-determined temperature is 420°C.
32. The claim as claimed in claim 28, wherein said first pre-determined temperature is 450°C.
33. The claim as claimed in claim 28, wherein heating rate is from 1 to 10 °C /
minute.
34. The claim as claimed in claim 28, wherein said pre-determined time is between 5 to 180 minutes.
35. The claim as claimed in claim 28, wherein said pre-determined time is 60 minutes.

36. The claim as claimed in claim 28, wherein said second pre-determined temperature is 150 to 250°C.
37. The claim as claimed in claim 28, wherein said rotor is an aluminium alloy die cast rotor.
38. The claim as claimed in claim 28, wherein said rotor is an aluminium alloy (LM6 grade) die cast rotor.
39. A rotor assembly made from treated aluminium alloy as claimed in any of the preceding claims.