FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patent Rules, 2003
Complete Specification
(See section 10 and rule 13)
A Method For Manufacturing Of Aluminum 6XXX Series Components
Bharat Forge Limited
An Indian company registered under the Indian Companies Act, 1956. Mundhwa, Pune - 411036, Maharashtra, India
The following specification particularly describes the invention and the manner in
which it is to be performed.

Field of invention
This invention relates to 6XXX series aluminum alloys. Particularly it relates to
the method of manufacturing of components made from 6XXX series Aluminum
alloys.
More Particularly this invention relates to the hot forging and heat treatment process for the manufacturing of components of the 6XXX series Aluminum alloys, carried out at temperatures above recrystallization temperatures of Aluminium.
Background of invention:
Aluminum alloys are most popularly used in the automotive industry because of their good formability, light weight and high strength after heat treatment. Currently the focus of the automotive industry is on controlling the environmental emission because of serious global warming issue. Hence, the automotive industry is focused on light weighting of the vehicles to improve the overall fuel efficiency. Significant efforts have been made to develop high strength Aluminum alloys to replace structural steel in current use.
Al-Mg-Si based 6XXX series heat treatable alloys have attracted automotive industry’s attention in recent years due to its attractive mechanical and corrosion properties. Alloying elements such as Mn, Cu and Cr are added in Al-Mg-Si alloys to improve mechanical and metallurgical properties of 6XXX series alloys.

6XXX series Aluminum alloys are strengthened by heat treatment (solution annealing and precipitation hardening treatment) through the presence of Mg and Si as major alloying elements.
The conventional component manufacturing process comprises hot forging the component (at about 450 °C) followed by heat treatment. The heat treatment comprises solutionising or solution treating or solution annealing the forged component at 500 °C to 550 °C for 2 hours and then water quenching it. This is followed by age hardening or artificial aging or precipitation hardening the water-quenched component at 170 °C to 200 °C for 10 hours and air cooling of the age-hardened component to the room temperature.
The purpose of solution annealing is to dissolve maximum possible amount of solutes in the solid solution. This process comprises soaking the alloy at a sufficiently high temperature for a long enough time to form a homogeneous solid solution. This is followed by Quenching, which is the most critical step. The purpose of quenching is not only to preserve the solid solution formed during solution annealing treatment but also to maintain a certain minimum number of vacant lattice sites to assist low-temperature diffusion required for GP zone formation. Following quenching, the component is subjected to aging to form precipitates that impart strength. The complete age hardening (also termed as precipitation hardening) treatment requires about 12.5 hours (including the heating time).

The drawbacks of the conventional method of manufacturing an Aluminum alloy are given below:
1. Microstructure is an important parameter to achieve desired mechanical properties. Conventional manufacturing process i.e. hot forging process followed by the heat treatment (i.e. solutionizing, quenching and precipitation hardening) very often causes recrystallized zones (with coarse grain structure) at the surface of component. Recrystallized zones generally form at the surface of the component which directly touches the die during hot forging. In recrystallized area, the grain structure gets coarsened during the post-forging cooling and solutionising heat treatment which leads to deterioration of mechanical properties.
2. The manufacturing process is very long and hence, cycle time for production of a component is large.
3. The energy required for the complete manufacturing process is also large. Energy is required for the heating of the Aluminum alloy for hot forging then again for the solution treatment and then again for the aging process. Further energy is required to maintain the component at high temperatures during solution treatment as well as artificial aging treatment.
The present invention discloses a method of manufacturing and an optimized heat treatment process for components made of 6XXX series Aluminum alloys used in automotive applications which overcomes above drawbacks of conventional manufacturing of components.

Objects of invention
Some of the objects of the present disclosure are as follows:
. It is an object of present invention to provide a method for manufacturing
components of 6XXX series Aluminum alloys. . It is another object of present invention to eliminate solution annealing
treatment in the manufacturing of 6XXX series Aluminum alloy
components. . It is yet another object of present invention to shorten the present age
hardening cycle time in the manufacturing of 6XXX series Aluminum
alloy components. . It is still another object of present invention to eliminate secondary
recrystallization in the manufacturing of 6XXX series Aluminum alloy
components. . It is further object of present invention to reduce the heat treatment cycle
time required in the manufacturing of 6XXX series Aluminum alloy
components. . It is still further object of present invention to establish energy efficient
and cost effective solution for manufacturing of 6XXX series Aluminum
alloy components..
Brief description of figures
Figure 1 shows the conventional manufacturing process for 6XXX series Aluminum alloy components.

Figure 2 shows invented manufacturing process for 6XXX series Aluminum alloy
components.
Figure 3 shows microstructure at the surface location of 6XXX series Aluminum
alloy component manufactured using conventional method of hot forging
followed by (T6) heat treatment process.
Figure 4 shows microstructure at surface location of 6XXX series Aluminum
alloy component manufactured according to the process of the invention.
Figure 5a and 5b shows the coarse recrystallized structure at surface location of
6XXX series Aluminum alloy component manufactured using conventional
process
Figure 6a and 6b shows fine recrystallized structure at surface location of 6XXX
series Aluminum alloy component manufactured according to the process of the
invention.
Summary of invention
The present invention is directed to a method of manufacturing components made from 6XXX series Aluminum alloys. The manufacturing process comprises hot forging of the 6XXX series Aluminum alloy component using various forging steps like preforming – blocker – Finisher – trimming – calibration. The component is still hot after completion of the above mentioned process. This hot forged part is immediately quenched in water or oil or polymer. This process is followed with a short term aging treatment which helps achieve the required properties in the component. The present innovative process of directly quenching

the forged parts after hot forging process in water/oil/polymer followed by short aging time within the specified temperature ranges offers significant improvement in properties of the 6XXX series Aluminum alloy component along with uniform grain structure as well.
Detailed description of invention
In accordance with the present invention, the drawbacks of convention manufacturing process have been overcome by the invented method of manufacturing of 6XXX series Aluminum alloy component. The method allows considerable material and energy savings as compared with the conventional process. Also, strength of the produced Aluminum component is uniform in view of conventional method.
6XXX Aluminum alloy forged and machined components are used extensively in automotive industry. Aluminum alloys of 6XXX series are particularly sought after in automotive industry due to their characteristic features like light weight, high corrosion resistance, good formability (extrusion and forging), good machinability and high strength subsequent to heat treatment.
Industrial practice involves induction heating of extruded bar followed by forging of 6XXX series Aluminum alloy Component in defined temperature range of 430-470 ºC. The conventional heat treatment (T6) process as shown in Figure 1 involves the strengthening of forged part through solution annealing and artificial

aging. The forged components are solutionized at 550 ºC for two hours and water quenched before artificial aging between 170-200 ºC for ten hours.
During conventional thermo-mechanical treatment of Aluminum 6XXX series alloy, coarse recrystallized areas are developed as shown in the Figure 3 at the surface of the forged parts after solution annealing. These areas of recrystallized coarse grain adversely impact the hardness, fatigue and corrosion resistance properties. The susceptibility to the formation of these coarse grain structures depends on forming and heat treatment parameters. Therefore, it is necessary to produce the part having the grain structure that does not allow recrystallization.
Figure 5a and 5b shows the non-uniform coarse recrystallized structure present at surface areas of components made form Aluminum 6XXX series alloy using conventional process. These coarse recrystallized structure formed in the surface layers are directly in-touch with forging dies and grows during the subsequent heat treatment.
In order to improve mechanical properties and achieve homogeneous grain structure, a new heat treatment process is developed by eliminating the Solution annealing process and conducting direct quenching immediately after completion of hot forging process. The forging process is designed in such a way that the temperature of these components at the end of forging process and before the direct quenching is above 470 ºC. Further this is followed by artificial aging with

shortened aging time as shown in Figure 4. The aging time depends upon the component’s section thickness and it ranges from 1 to 4 hrs. There is reduction in aging time by about 60 to 90% as compared to conventional process.
Figure 6a and 6b shows the microstructure present at surface areas of components made form Aluminum 6XXX series alloy using invented manufacturing process. In this method, direct quenching after hot forging results in very small or indistinctive recrystallized area which is observed near the surface layers of the component and elimination of solution annealing in heat treatment hinders the growth of this recrystallized structure.
In accordance with one embodiment of the present invention there is provided a method of manufacturing a 6XXX series Aluminum alloy component as shown in Figure 2, said method comprises the following steps:
1. 6XXX series Aluminum alloy billet heating (Minimum 470 °C) in induction heater. Alternatively, the billet can be heated in fuel fired or electric furnace. The output of this process is a heated billet.
2. Hot forging of the heated billet which involves various steps like preforming, blocker forging, finisher forging, Trimming and/or padding/calibrating. These steps are carried out in a forging equipment (either press or hammer), capable of generating enough energy and force. The output of this process is a hot forged part. The forging process is

designed in such a way that the temperature of the hot forged part is above 470 ºC.
3. Quenching of the hot forged part directly after the hot forging process in agitated bath or quench tank. The transfer time from hot forging station to quenching station is maintained such that the hot forged part temperature does not drop below 470 °C before start of quenching. The quenching medium in the bath or quench tank can be water, oil or polymer mix for quenching purpose. The output of this process is a solutionised part.
4. Aging of the solutionised part at 170-200° C for 1-4 hours in an electrical heating furnace followed by air cooling to room temperature. Alternatively the aging heat treatment can be performed in a fuel fired furnace also. The output of this process is an aged component.
5. Performing the post forging treatment on the aged part like shot blasting etc. The output of this process is a treated part.
6. Performing machining operations on the treated part to obtain a 6XXX series Aluminum Alloy component.
Example
As shown in Figure 1, conventionally, EN AW 6082 (Aluminum Alloy Grade from 6XXX series) extruded round bars of 250 mm length with diameter of 80 mm are heated to around 430 to 470 ºC and are forged on 2500 ton forging press. After forging, the forged components are allowed to cool in natural air. The forged components are then solutionised at 550 °C for 2 hours and water

quenched immediately. Next, they are artificially aged at a temperature of around 170 to 200 ºC for 10 hrs.
Figure 3 shows microstructural image of coarse recrystallized areas developed at the surface of above forged component after solution annealing using conventional method. These areas of recrystallized coarse grains adversely impact the hardness, fatigue and corrosion resistance properties.
In the invented method, EN AW 6082 (Aluminum Alloy Grade from 6XXX series) extruded round bars of 250 mm length with diameter of 80 mm are heated to minimum of 470 ºC and are hot forged. The forging process is designed in such a way that the temperature of these components at the end of forging process is above 470 ºC. These forged components are quenched in water immediately after the hot forging operation and are then artificially aged at 170 ºC for 2 hrs. The time consumed in transferring the hot forged component from press to quench tank is around 20-25 seconds.
Figure 4 shows microstructural image showing absence of recrystallization grains at the surface of above forged component using newly developed method which results in improved dynamic performance at surface location.
Technical advance made by and economic significance of invention The invented process leads to following benefits:

1) Effective Alternative Process
a) Elimination of separate solution heat treatment process and reduction in aging treatment time which further reduces the energy consumption during the manufacturing process.
b) Reduction of cycle time minimizes the operating cost and hence, leads to overall cost saving.
2) Surface Quality
a) The invented process produces finer grain size and microstructure near the surface of the manufactured component (see Figures 5 and 6).
b) Non uniform and coarse recrystallized grains at surface of component are eliminated which results in improved dynamic performance (see Figure 6).

3) The invented process leads to improved static and dynamic properties in the manufactured components.
4) The invented process leads to heat treated fine grain structure resulting in a desired combination of ductility and strength.
5) The present invention provides desired mechanical properties in a short processing time and an additional benefit of better Inter Granular Corrosion (IGC) resistance.

We claim:
1. A method for manufacturing of Aluminum 6XXX series alloy component
characterised in that said method comprising the steps of:
a. heating a billet made of Aluminum 6XXX series alloy to produce a heated
billet;
b. hot forging said heated billet to produce a hot forged component;
c. quenching said hot forged component in an agitated bath or quench tank to
produce a solutionised component;
d. carrying out aging of the solutionised component for a predetermined time
period followed by air cooling to produce an aged component;
e. performing post forging treatment on the aged component to produce a
treated component;
f. machining said treated component to obtain a final Aluminum 6XXX
series Alloy component.
2. A method as claimed in claim 1 wherein the billet heating of step a is carried out in an induction heater or in a fuel-fired or electric furnace to a minimum temperature of 470 °C.
3. A method as claimed in claims 1 to 2, wherein the hot forging process of step b of claim 1 comprises any of the processes including preforming, blocker forging, finisher forging, trimming and/or padding/calibration carried out in a forging equipment, and wherein the temperature of hot forged component is greater than 470 °C.

4. A method as claimed in claims 1 to 3, wherein the step c of quenching is carried out using any of the quenching media including water, oil, or polymer mix, and wherein the transfer time from hot forging station to quenching station is maintained to keep the temperature of said hot forged component above 470 °C before start of quenching.
5. A method as claimed in any of claims 1 to 4, wherein in said step d, the aging process is carried out at a temperature between 170 - 200 °C.
6. A method as claimed in any of claims 1 to 5, wherein in said step e said predetermined period is between 1-4 hours.
7. A method as claimed in any of claims 1 to 6, wherein said post forging treatment of step g of claim 1 includes shot blasting.

A Method For Manufacturing Of Aluminum 6xxx Series Alloy Component