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. 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