US20160130686A1

US20160130686A1 - Aluminum alloy composition and heat treatment method of the aluminum alloy composition

Info

Publication number: US20160130686A1
Application number: US14/991,722
Authority: US
Inventors: Nak-Young Kim
Original assignee: Hyundai Motor Co
Current assignee: Hyundai Motor Co
Priority date: 2012-10-05
Filing date: 2016-01-08
Publication date: 2016-05-12
Also published as: US20140096879A1; KR20140044488A; CN103710584A

Abstract

Disclosed herein is an aluminum alloy composition and a method of heat treating the aluminum alloy, to improve process control and strength of the aluminum alloy for a rear safety plate mounted on a truck, etc., complying with safety regulations wherein the aluminum alloy composition includes Silicon (Si) about 0.8 to 1.3% by weight, Iron (Fe) up to about 0.5% by weight, Copper (Cu) about 0.15 to 0.4% by weight, Manganese (Mn) up to about 0.15% by weight, Magnesium (Mg) about 0.8 to 1.2% by weight, Chromium (Cr) up to about 0.25% by weight, Zinc (Zn) up to about 0.2% by weight, Titanium (Ti) up to about 0.1% by weight and the remaining percent by weight of Aluminum (Al) of the entire composition.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2012-110499, filed on Oct. 5, 2012, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

(a) Technical Field
The present invention relates to an aluminum alloy composition and a method of heat treating the aluminum alloy composition, and more specifically, to the aluminum alloy composition and the heat treatment method for a process control and strength improvement of the aluminum alloy used for rear safety plates mounted to large trucks, etc., in compliance with safety regulations.
(b) Background Art
Generally, aluminum (Al) is die casted easily and is alloyed easily with other metals, and wherein the die casting and alloy process are performed at room and high temperature without difficulty. Further, the aluminum exhibits high corrosion resistance and high electrical and heat conductivity and is thereby widely used in the industry.
Recently, aluminum has been widely used for reducing weight of a vehicle, thereby improving fuel efficiency. However, since aluminum itself does not have high strength compared to other metals, an aluminum alloy which includes other metals to improve the overall strength of the alloy has been widely used.
FIG. 1 is an exemplary view illustrating a rear safety plate according to the related art, and FIG. 2 is an exemplary sectional view illustrating a portion of the rear safety plate taken along line A-A′ in FIG. 1 wherein as shown in the drawings, the rear safety plate includes a guard having a length corresponding to a width of a vehicle, a stay configured to support the guard and holds the guard to a chassis of the vehicle, and a reinforcing material to improve the strength.
The rear safety plate is mounted on a vehicle to prevent damage to a vehicle body or a driver by bending into the lower part of a truck when a vehicle with low height collides with a back side of the truck, wherein the rear safety plate must satisfy the strength level designated by the present safety regulations.
A guard of a conventional rear safety plate is generally manufactured by a T6 Heat Treating process (e.g., age hardening after solution heat treatment) of an aluminum extrusion material A6061 to reduce the vehicle weight and improve vehicle marketability. However, some of the guards do not satisfy the strength level regulations due to a low safety ratio and high strength variations according to heat treatment conditions such as temperature and duration of heating.
In addition, in the T6 Heat Treatment process of the conventional aluminum extrusion material A6061, physical properties are deteriorated due to coarse growth of precipitations for a long aging time thereby increasing process cost.
Moreover, a steel rein is used as a reinforcement material to rectify strength variations according to heat treatment conditions; however, the addition of the reinforcement material increases an overall vehicle weight policy on shaft weight of a large truck.
The description provided above as a related art of the present invention is just for helping understanding the background of the present invention and should not be construed as being included in the related art known by those skilled in the art.

SUMMARY OF THE DISCLOSURE

The present invention provides an aluminum alloy composition and a heat treatment method of an aluminum alloy from which a guard of a rear safety plate is made. Specifically, an aging heat treatment condition and composition are optimized to reduce heat treatment time and improve uniform strength and size of the aluminum alloy, and thus reducing the weight by removing reinforcing material.
An aluminum alloy composition according to the present invention includes Silicon (Si) about 0.8 to 1.3% by weight, Iron (Fe) up to about 0.5% by weight, Copper (Cu) about 0.15 to 0.4% by weight, Manganese (Mn) up to about 0.15% by weight, Magnesium (Mg) about 0.8 to 1.2% by weight, Chromium (Cr) up to about 0.25% by weight, Zinc (Zn) up to about 0.2% by weight, Titanium (Ti) up to about 0.1% by weight and the remaining percent by weight of Aluminum (Al) of the entire composition.
Further, the aluminum alloy composition according to an embodiment of the present invention further includes Beryllium (Be) and Zirconium (Zr). Additionally, the Beryllium (Be) is about 0.04 to 0.07% by weight and the Zirconium (Zr) is about 0.2 to 0.3% by weight.
A heat treatment method of an aluminum alloy composition is performed to improve strength through a solution heat treating process of the aluminum alloy composition and aging heat treating process wherein the aging heat treatment is maintained at about 205-215° C. for 4 to 5 hours.
Moreover, the aluminum alloy composition comprises the elements as described-above. Further, the aging heat treatment may be maintained at about 210° C. for 5 hours. In addition, the solution heat treatment is maintained at about 520° C. to 560° C. for 1.5 to 2.5 hours. Alternatively, the solution heat treatment is maintained at about 540° C. for 2 hours.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will now be described in detail with reference to exemplary embodiments thereof illustrated the accompanying drawings which are given herein below by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is an exemplary view illustrating a rear safety plate, according to the related art;

FIG. 2 is an exemplary sectional view illustrating a part of the rear safety plate taken along line A-A′ in FIG. 1, according to the related art;

FIG. 3 is an exemplary diagram illustrating a T6 Heat Treatment process, according to the related art;

FIG. 4 is an exemplary graph illustrating hardness variations according to aging time and temperature of an existing aluminum alloy A6061;

FIG. 5 is an exemplary diagram illustrating hardness value according to aging treatment time at the heat treatment of the existing aluminum alloy A6061;

FIG. 6 is an exemplary graph illustrating the T6 Heat Treatment including an aging treatment according to an exemplary embodiment of the present invention; and

FIG. 7 is an exemplary diagram illustrating a strength test method of the rear safety plate.

It should be understood that the accompanying drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.
In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, combustion, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum).
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Unless specifically stated or obvious front context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for ex ample within 2 standard deviations of the mean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term “about.”
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
The present invention relates to an aluminum alloy composition with improved strength by adjusting the composition ratio and adding new alloy elements. Aluminum alloys may be classified into 1000 Series to 8000 Series according to type and amount of metal to be mixed with the alloy wherein the aluminum alloy is classified into: 1000 Series of pure aluminum (Al) of more than about 99.0%; 2000 Series of an alloy series of aluminum (Al) and Copper (Cu); 3000 Series of an alloy series of aluminum (Al) and Manganese (Mn); 4000 Series of an alloy series of aluminum (Al) and Silicon (Si); 5000 Series of an alloy series of aluminum (Al) and Magnesium (Mg); 6000 Series of an alloy series of aluminum (Al), Magnesium (Mg) and Silicon (Si); 7000 Series of an alloy series of aluminum (Al), Zinc (Zn) and Magnesium (Mg); and 8000 Series of an alloy series of aluminum (Al) and other elements.

TABLE 1

Description	Si	Fe	Cu	Mn	Mg	Cr	Zn	Ti	Be	Zr	Al

A6061	0.40-0.80	0.7 or	0.15-0.40	0.50 or	0.8-1.2	0.04-0.35	0.25	0.15	—	—	Remainder
		less		less
A6082	0.7-1.3	0.50	0.10	0.40-1.0	0.6-1.2	0.25	0.20	0.10	—	—	Remainder
		or less
Present	0.80-1.30	0.50	0.15-0.40	0.50 or	0.8-1.2	0.25 or	0.20	0.10	0.04-0.07	0.20-0.30	Remainder
invention		or less		less		less	or less	or less

The above Table 1 shows a comparison of a conventional aluminum alloy composition and an aluminum alloy composition according to an exemplary embodiment of the present invention (unit weight %).
The aluminum alloy composition according to the present invention may comprise: Silicon (Si) about 0.8 to 1.3% by weight, Iron (Fe) up to about 0.5% by weight, Copper (Cu) about 0.15 to 0.4% weight. Manganese (Mn) up to about 0.15% by weight, Magnesium (Mg) about 0.8 to 1.2% by weight, Chromium (Cr) up to about 0.25% by weight, Zinc (Zn) up to about 0.2% by weight, Titanium (Ti) up to about 0.1% by weight and the remaining percent by weight of Aluminum (Al) of the entire composition.
In other words, comparing to the conventional aluminum alloy composition A6061, the aluminum alloy composition according to the present invention changes the content of Silicon (Si), etc., and further may add Beryllium (Be) and Zirconium (Zr) to improve the strength by forming a proper amount of Mg2Si precipitation phase during a heat treatment to create an age hardening.
In particular, in the aluminum alloy composition according to the present invention, the content of Silicon (Si) may be increased to precipitate sufficiently the Mg2Si phase, in comparison to the conventional aluminum alloy composition A6061 wherein when the content is less than 0.80% by weight, the Mg2Si phase is precipitated at a small amount to not effect the age hardening, and when the content of Silicon (Si) exceeds 1.30% by weight, the Mg2Si phase is precipitated excessively decreasing the toughness of the material.
Further, when the content of the Iron (Fe) exceeds about 0.50% by weight, the Al3Fe compound may be formed to crystallize an inter-metallic compound of a needle type. Further, Beryllium (Be) may be added to increase the strength and toughness of the aluminum alloy composition through uniformly distributing the precipitation, wherein when the content of the Beryllium (Be) is below about 0.04% by weight, it is insufficient to achieve the effect as described above, and when the content of the Beryllium (Be) exceeds about 0.07% by weight, segregation may occur due to low solid solution level to Aluminum (Al), thereby deteriorating mechanical properties of the composition.
Moreover, the Zirconium (Zr) may be added to increase the strength through reducing the granularity of grains by precipitating a fine inter-metallic compound wherein when the content of the Zirconium (Zr) is less than about 0.1% by weight, the inter-metallic compound is not precipitated, and when the content of the Zirconium (Zr) exceeds about 0.3% by weight, a coarse inter-metallic compound is precipitated thereby deteriorating physical properties of the composition.
The present invention relates to a heat treatment method of an aluminum alloy composition with optimizing aging conditions, shortening heat treatment.
As described above, aluminum alloys may be classified into 1000 Series to 8000 Series according to type and amount of metal mixed to the Aluminum Series. In particular, the aluminum alloys may be classified into heat treatment alloys (e.g., 2000, 6000 and 7000 Series) and non-heat treatment alloys (e.g., 1000, 3000, 4000 and 5000 Series) according to whether a heat treatment process may be performed to the aluminum alloy.
The heat treatment aluminum alloy of 2000, 6000 and 7000 Series may be heat treated variously to attain the required physical property values by increasing the strength or removing stress. Types and methods of general heat treatment processes are described in the following Table 2.

TABLE 2

Type	Method

T1	Naturally aging heat treated after cooling from a high temperature
	processing
T2	Processed and aging heat treated naturally again after cooling from
	high temperature process
T3	Cold processed and aging heat treated naturally again after solution
	heat treatment
T4	Naturally aging heat treated after solution heat treatment
T5	Artificially age hardened after cooling from high temperature
	processing
T6	Artificially age hardened after solution heat treatment
T7	Stabilized after solution heat treatment
T8	Cold processed and artificially age hardened again after solution
	heat treatment
T9	Artificially age hardened again and cold processed after solution
	heat treatment
T10	Cold processed artificially age hardened again after cooling
	from high temperature processing

Among such heat treatment processes, Method T6 is a typical heat treatment method used in a heat treated aluminum alloy to improve hardness or mechanical strength of aluminum alloys. A conventional T6 heat treatment process is shown in FIG. 3. In other words, according to a prior art, even though there are variations depending on types and amount of mixing metals and shapes of parts used, the composition of aluminum alloy A6061 is heat solution treated to manufacture a guard of a rear safety plate at about 520° C. to 560° C. for 1.5 to 2.5 hours and then aging heat treated at the temperature of about 185° C. (T2) for 8 hours.
Furthermore, in the solution heat treatment, the composition may be heated at a melting temperature or greater to melt the alloy element in the aluminum alloy and cooled abruptly after a predetermined time to create a supersaturated solid solution wherein an optimal temperature (T1) for the solution heat treatment of the aluminum alloy A6061 is 540° C. and optimal time is 2 hours.
Further, the aging heat treatment is a process configured to precipitate the alloy elements which are solid solution supersaturated to the matrix to determine physical properties of a material. Accordingly, it may be necessary to set an optimized value of each parameter since physical properties such as strength may vary depending on conditions such as time and temperature of the aging heat treatment in maintenance section (hereinafter, conditions for solution heat treatment are identical to those of conventional solution heat treatment).

TABLE 3

Aging
Treatment	Maximum Strength	Minimum Strength

Temperature		Tensile	Conversion		Tensile	Conversion
(□)	Hardness (Hv)	Strength (MPa)	Coefficient	Hardness (Hv)	Strength (MPa)	Coefficient

0	95.4	331.44	2.82	95.4	331.44	2.82
175	106.28	387.24	2.69	71.76	201.96	3.48
185	121.60	432.84	2.76	78.14	304.57	2.51
195	117.06	342.28	3.35	81.35	285.02	2.80
220	117.16	336.03	3.42	73.87	315.81	2.29

Meanwhile, hardness and tensile strength are shown according to aging heat treatment temperature of aluminum alloys wherein as shown in the above table, the hardness and the tensile strength are linearly proportional and thus, an aging heat treatment condition showing optimal tensile strength by comparing the hardness values will be described.
FIG. 4 is an exemplary graph showing changes in hardness according to time and temperature of the aging heat treatment of an existing aluminum alloy A6061 wherein the measurement result of the hardness according to temperature shows that maximum hardness occurs when the aging heat treatment temperature is 185° C. to 220° C. and to determine optimal aging heat treatment time, hardness may be measured again within the temperature range of the aging heat treatment.

TABLE 4

Aging
heat
treat-
ment
temper-
ature	Time (h)

(° C.)	2	3	4	5	6	7	8	9	10

185	92	96	106	113	121	128	134	140	141
195	96	99	108	119	128	131	139	136	133
205	105	111	126	133	138	139	137	134	131
215	118	124	131	138	137	133	126	121	123
220	123	134	140	119	103	110	106	104	105

Table 4 and FIG. 5 show hardness values according to time of the aging heat treatment when the existing aluminum alloy A6061 is heat treated wherein hardness values according to the respective aging heat treatment times are shown when the aluminum alloy is solution heat treated at 540° C. for 2 hours and then at 185° C. to 220° C. for 2 to 10 hours.
As shown in the above table, the hardness of an aluminum alloy varies according to the temperature and time of the aging heat treatment. When the temperature of the aging heat treatment is 220° C., the table shows variations in the hardness and when the time of the aging heat treatment exceeds 3 hours, the hardness is abruptly decreased.
Further, when the temperature of the aging heat treatment is 185° C. to 195° C., the time of the aging heat treatment and the hardness level are generally proportional to each other and thus to obtain a sufficient hardness, the time of the aging heat treatment may be increased.
Accordingly, the temperature of the aging heat treatment may be within a range of 205° C. to 215° C. maintained for about 4 to 5 hours (Target Hardness Section), and the process cost may reduce due to a decrease in the aging heat treatment time while exhibiting a satisfactory hardness within the temperature range.
In other words, considering easy process control, heat treatment time and superior tensile strength corresponding to maximum hardness, an aging heat treatment condition may maintain temperature within 205° C. to 210° C. for 4 to 5 hours, and alternatively, at 210° C. for 5 hours. (e.g., Solution heat treatment conditions are identical to those of conventional solution heat treatment).

TABLE 5

						Average
						Tensile
Description	#
1	#2	#3	#4	#5	Strength (MPa)

Embodiment 1	441	444	459	455	451	450
Embodiment 2	451	449	461	452	461	455
Embodiment 3	453	460	449	459	455	455

Table 5 above shows the measurements of tensile strength measured from 5 specimens according to the respective Embodiments 1 to 3 which meet the aging heat treatment conditions of the present invention, and FIG. 6 is an exemplary graph showing a T6 Heat Treatment. The T6 Heat Treatment includes the aging heat treatment of the present invention wherein the average tensile strength was measured as 450 MPa. 455 MPa and 455 MPa from the heat treatment, respectively. In each embodiment, aging heat treatment temperature is 210° C., and aging heat treatment time is 5 hours.
In other words, as a result of the heat treatment of the present invention, an aluminum alloy with high tensile strength may be yielded and thus, there is almost no difference in tensile strength and it may be unnecessary to use any reinforcing material to compensate for the difference.
FIG. 7 is an exemplary view showing a strength test method of the rear safety plate. Loads may be applied in a sequence based on the order of P3, P1(LH), P1(RH), P2(LH) and P2(RH), and the result is shown in the following Table 6.

TABLE 6

Legal	Target
Load	Load	Conventional material	Developed material

Description	(kg)	(kg)	Comparison 1	Comparison 2	Comparison 3	Em. 4	Em. 5	Em. 6

P3	2549	3117	2658	2642	2659	3166	3325	3188
P1(LH)	2549	3058	2632	2631	2651	3070	3287	3097
P1(RH)			2632	2637	2651	3070	3287	3097
P2(LH)	10193	12232	10483	10412	10384	12233	12849	12315
P2(RH)			10476	10419	10386	12237	12843	12327

Table 6 shows test evaluations of the materials performed through the conventional heat treatment (e.g., solution heat treatment at 540° C. for 2 hours and aging heat treatment at 185° C. for 8 hours) and the heat treatment (e.g., solution heat treatment at 540° C. for 2 hours and aging heat treatment at 210° C. for 5 hours) according to an exemplary embodiment of the present invention.
In other words, the conventional material satisfies legal load but fails to satisfy the target load, causing deformation to a guard of a safety plate, however the material that is heat treated according to the present invention satisfies both the legal load and the target load causing no deformation to the guard, thereby improving strength.
According to the present invention, the heat treatment condition and composition of an aluminum alloy from which a guard of a rear safety plate is formed are optimized, thereby controlling easily processing and improving strength to comply with the related regulations.
Further, according to the present invention, vehicle weight may be reduced and manufacturing cost of the guard may decreases by removing a reinforcing material used in the prior art to improve strength.
Moreover, according to the present invention, a conventional aging heat treatment time may be reduced to shorten the entire process time and reduce manufacturing cost and improve vehicle marketability through the use of aluminum alloy rear safety plate having high corrosion resistance compared with steel products.
The invention has been described in detail with reference to exemplary embodiments thereof. However, it will be appreciated by those skilled in the art that changes or modifications may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the accompanying claims and their equivalents.

Claims

1-3. (canceled)

4. A heat treatment method of an aluminum alloy composition, comprising:

heat treating the aluminum alloy; and

after heat treating the aluminum alloy, age heat treating the aluminum alloy at about 205° C. to 215° C. for 4 to 5 hours.

5. The heat treatment method of claim 4, wherein the aluminum alloy composition comprises Silicon (Si) about 0.8 to 1.3% by weight, Iron (Fe) up to about 0.5% by weight, Copper (Cu) about 0.15 to 0.4% by weight, Manganese (Mn) up to about 0.15% by weight, Magnesium (Mg) about 0.8 to 1.2% by weight, Chromium (Cr) up to about 0.25% by weight, Zinc (Zn) up to about 0.2% by weight, Titanium (Ti) up to about 0.1% by weight and the remaining percent by weight of Aluminum (Al) of the entire composition.

6. The heat treatment method of claim 5, wherein the aluminum alloy composition further comprises Beryllium (Be) and Zirconium (Zr).

7. The heat treatment method of claim 6, wherein the Beryllium (Be) is about 0.04 to 0.07% by weight and the Zirconium (Zr) is about 0.2 to 0.3% by weight of the entire composition.

8. The heat treatment method of claim 4, further comprising: age heat treating the aluminum alloy at 210° C. for 5 hours.

9. A heat treatment method of claim 4, further comprising: solution heat treating the aluminum alloy at about 520° C. to 560° C. for 1.5 to 2.5 hours.

10. The heat treatment method of claim 9, further comprising: solution heat treating the aluminum alloy at 540° C. for 2 hours.

11. (canceled)