Recent Development and Applications of Magnesium Alloys in the

Materials Transactions, Vol. 49, No. 5 (2008) pp. 894 to 897
Special Issue on Platform Science and Technology for Advanced Magnesium Alloys, IV
#2008 The Japan Institute of Metals
Recent Development and Applications of Magnesium Alloys
in the Hyundai and Kia Motors Corporation
Jae Joong Kim* and Do Suck Han
Materials Research Team, Advanced Technology Center, Research & Development Division for Hyundai Motor Company
& Kia Motors Corporation, 772-1, Jangduck-Dong, Hwaseong-Si, Gyeonggi-Do, 445-706, Korea
Recent legislative and environmental pressures on the automotive industry to produce light-weight fuel efficient vehicles with lower
emissions have led to a requirement for traditional steel components to be replaced by advanced materials such as aluminum, magnesium and
metal matrix composites. This has led to a complete re-analysis of engineering design and manufacturing routes, with the emergence of
advanced technologies as a viable process for the production of high volume, low cost, high integrity automotive components. Here we present a
general review of the application of magnesium alloys for the automotive components. We will also discuss the research activities and
application of magnesium alloys and key technologies including the successful development of magnesium seat frame described and discussed
in terms of vehicle performance and casting qualities introduced in vehicles developed by the Hyundai and Kia motors corporation
(HKMC). [doi:10.2320/matertrans.MC200731]
(Received October 5, 2007; Accepted December 10, 2007; Published January 30, 2008)
Keywords: automotive component, magnesium seat frame, vehicle performance
1.
General Review of Automotive Application
Automotive makers have focused on application of
magnesium alloys to automotive components since the early
1990s, in terms of fuel efficiency and weight reduction.1,2)
Since then in the area of powertrain, interior, chassis and
body parts the magnesium parts have been applied successfully as a result of advanced engineering design, alloy
development and die-casting technology. Though many
magnesium parts have been mass-produced in the automobiles, few parts are widely used. Namely, such parts can be
indicated as steering wheel core and instrument panel (or
cowl cross beam) in the interior part, and engine head cover
in the powertrain parts. Additional parts can be steering
column housing, seat frame, intake manifold system and
manual transmission case in the automotive parts.
In Europe, powertrain parts have been actively developed
for high class platform, whose significant weight of magnesium parts is approximately 10 kg on average. In North
America, interior parts have been actively developed for
luxury car and utility vehicle, whose significant weight of
magnesium parts is approximately 15 kg on average. In
Korea and Japan, interior and powertrain parts have been
developed for luxury sedans, whose significant weight of
magnesium parts is approximately 8 kg on average.
The automotive parts with high temperature magnesium
alloys, such as engine block, engine cradle, etc., have shown
up recently, and are expected to be widely used in the near
future.3,4) On the other hand, application of magnesium
wrought alloys has been interesting to the automotive
makers, which have presented some developed parts without
mass production yet.5) In the wrought alloy, it will be
necessary to reduce high cost of material and process to enter
the competitive market.
*Corresponding
author, E-mail: [email protected]
2.
Research and Development (R & D) Activities of
HKMC
2.1 Introduction to Magnesium Mass Products
HKMC has also actively carried out research on the
application of the magnesium parts for its automotive
platforms. The R & D demonstrated that magnesium alloy
can be substituted for steel, aluminum and zinc alloys in the
interior part. For example, magnesium seat frame, steering
wheel core, steering column housing, lock body and driver
air-bag housing are shown in Figs. 1(a)–(e) respectively. It is
interesting to note that approximately 80% of the steering
wheel core in HKMC is made of magnesium alloy, AM50A.
Five such parts are manufactured by die-casting process.
More recently, a couple of interior parts have been developed
by die-casting and will be launched for mass-production at
the end of 2007.
On the other hand, Fig. 2(a) shows the first thixotropicmolded part launched for Hyundai luxury utility vehicle
(LUV). This part is the painted frame with clean surface for
the navigation system as shown in Fig. 2(b). It is well known
that thixo-molding process is an eco-process that minimizes
casting defect.
HKMC keeps working on application of magnesium diecast part to meet the need for higher fuel efficiency. Figure 3
shows that those automotive parts, mentioned above in Fig. 1
have already been used for Hyundai Azera (Grandeur) and
Kia Amanti (Opirus), and will be used for Hyundai Genesis.
As shown in Figs. 3(a)–(c) respectively, the applied weight
of magnesium parts is approximately 7.6 kg, 8.2 kg and 7.8 kg
in order. Moreover, a new magnesium part will be added in
the Hyundai Genesis.
2.2 Development of Front Seat Frame
Magnesium seat frame is meaningful to HKMC in terms of
weight savings and bolstering the magnesium industry.
HKMC projects approximately a 6 kg weight reduction in
the front seat system per car with approximately 3,700 tons
Recent Development and Applications of Magnesium Alloys in the Hyundai and Kia Motors Corporation
(a)
(b)
(c)
(d)
895
(e)
Fig. 1 Magnesium interior parts used in HKMC: (a) Seat frame, (b) steering wheel core, (c) steering column housing, (d) lock body and
(e) driver air-bag housing.
(a)
(b)
(a)
(b)
Fig. 2 Thixotropic molded magnesium parts for Hyundai LUV: (a) Painted
frame for (b) interior design with navigation system.
concurrently consumed per year in 2007, comparing to
approximately 670 tons per year in 2004. The magnesium
seat frame, including back frame as well as cushion frame,
has been successfully developed for HKMC luxury sedan.
Figure 4(a) shows a representation of a back frame made of
AM50A. Here we see a 40% weight reduction (approximately 6 kg) by exchanging material from steel to magnesium alloy with concurrent part reduction (18 ! 2 pieces) by
exchanging the process of pressing and welding to diecasting. Therefore, we can accomplish process consolidation
as well as weight reduction. Most of all, it is meaningful that
we can integrate the directly connected structure between
magnesium back frame and magnesium cushion frame (see
Fig. 1(a) in detail) for the front power-moved seat system for
both driver and passenger, as shown in Fig. 4(b), because the
engineering design is related to crash performance.
The development process consists of engineering design,
computer-aided engineering (CAE), flow simulation (die
casting) and crash performance simulation (real test) as
shown in Fig. 5. Pre-study on the modular design concept,
CAE and flow simulation was previously presented.6) Here,
the design objectives are one piece die-cast Mg structure
substituted for previous welded steel structure, the minimized
change of assembly related parts, and the maintenance of
(a)
(b)
Fig. 4 (a) A representation of magnesium back frame and (b) front seat
system for driver and passenger.
Fig. 5
Development process of magnesium seat frame in this work.
stiffness and impact absorption of the steel press parts. The
most important design is the optimized recliner mounting
part based on structural and casting analysis resulting in the
directly connected structure between back frame and cushion
(c)
Fig. 3 Platforms with significant weight of magnesium parts in HKMC: (a) Hyundai Azera (Grandeur), (b) Kia Amanti (Opirus) and (c)
Hyundai Genesis.
896
J. J. Kim and D. S. Han
imately 2.5 mm. The result of coupon tensile test on as-cast
back frame shows a reasonable stress-strain behavior without
casting defect. It is essential to meet safety regulation test for
commercialized seat system. We simulate the test with a full
car model using finite element method on the final design
before performing the real crash test on magnesium seat
assembly. The regulation tests on the magnesium seat
assembly have successfully concluded.
We carried out computed fluid dynamics analysis for
tooling design of back frame and cushion frame to accomplish the sound magnesium casting. It is well known that
molten metal of magnesium has less latent heat than that of
aluminum. That is the reason why we choose the center gate
system instead of the bottom gating system relating temperature drop of molten metal. Also one of the most important
factors with respect to keeping better fluidity can be die
temperature and gating speed. Both back frame and cushion
frame have the relative thin wall and wide projection area for
casting.
(a)
250
Stress (MPa)
200
S1
S2
S3
S4
150
100
50
0
0
2
4
6
8
10
12
14
Strain (%)
(b)
250
Stress (MPa)
200
SS1
SS2
SS3
150
100
50
0
0
2
4
6
8
10
12
14
Strain (%)
(c)
250
Stress (MPa)
200
U1
U2
U3
U4
U5
150
100
50
0
0
2
4
6
8
10
12
14
Strain (%)
Fig. 6 Coupon tensile test on important local parts in magnesium back
frame showing stress-strain curves obtained from (a) inner side frame, (b)
outer side frame, and (c) top area, respectively.
frame. To reach the objectives, AM50A is selected due to its
good ductility (as shown in Fig. 6) and the average thickness
of magnesium back frame and cushion frame is approxExtrusion
2.3 R & D Strategic Work
R&D strategy of HKMC is similar to world trends of
magnesium application technology. We can classify the
application technology in three distinct areas: modular
design, high temperature alloy, and wrought process. Firstly,
we have worked on modular design for one-piece casting,
such as seat frame, cowl cross beam and so on. Secondly, we
are working on development and application of high temperature alloy. In the powertrain part, all of transmission case is
produced by aluminum die-casting, but recently magnesium
manual transmission case and engine head cover have been
successfully developed using AZ91D alloy. Automotive
transmission case, engine oil pan and cylinder block for V6
engine are being developed using high temperature alloys to
reach 12 kg weight reductions. This evaluation and development of high temperature alloys have been co-worked with
research institutes and universities in Korea. Thirdly, HKMC
Bending
Welding
Fig. 7 Rear seat back frame manufactured by extrusion, bending and welding.
Recent Development and Applications of Magnesium Alloys in the Hyundai and Kia Motors Corporation
continues its application of wrought alloy. For example, rear
seat back frame was made of extruded alloy, AZ31 by
bending and welding as shown in Fig. 7. The dash panel was
sheet-pressed at elevated temperature. As shown, HKMC
continues to develop across these three technology areas of
modular design, high temperature alloy, and wrought
process.
3.
897
automotive industry to produce lighter and more fuel efficient
vehicles.
Acknowledgements
Authors give many thanks to engineers who have
contributed to the work mentioned in this paper.
Application in Future
Magnesium automotive parts continue to increase due to
need for weight reduction and high performance. Modular
design of one-piece magnesium casting shows stable increase
in usage due to weight reduction and process consolidation.
High temperature alloys continue to be applied to powertrain
parts, such as engine oil pan, automotive transmission case
and cylinder block. Even R & D into wrought alloy
application, promises greater cost reduction to make those
applications economically feasible over broad platforms. In
essence, the use of magnesium will continue to be developed
to address the legislative and environmental pressures on the
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