F2008SC031MAGNESIUM: THE WEIGHT SAVING OPTION1    Guillén Abásolo, David*,1    University of Burgos, SpainKEYWORDS – Elect...
In 2006, production of primary magnesium in the world was approximately 726.000 metrictons. As shown in figure 1, evolutio...
PROPERTIES PURE OF MAGNESIUM                  Property                         Conditions             Measure         Comm...
3. New alloys: AM-lite, HyMag 1, HyMag 2, MRI 153M, MRI 230D   4. Other: AS21, AS21X, AS41MANUFACTURINGMg-alloy component ...
Traditionally the Workhorse alloy has been Mg-Al and most of the alloys used are typesAZ91 because it shows superior casta...
Magnesium applicationsMg-alloys are very attractive in applications for the automotive, railway and aerospaceindustries as...
Figure 6: Factors influencing the corrosion properties of Mg-AlloysGalvanic Corrosion (GC)GC occurs when magnesium is conn...
Smoothing by polishing, honing, grinding or    Methods of pre-            Mechanical                                      ...
CONCLUSION, AUTOMOTIVE APPLICATIONEnvironmental conservation is one of the principal reasons for the focus of attention on...
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Magnesium weight saving option

  1. 1. F2008SC031MAGNESIUM: THE WEIGHT SAVING OPTION1 Guillén Abásolo, David*,1 University of Burgos, SpainKEYWORDS – Electrolytic process, Thermal reduction, lightest, reactive, Surfacestreatments, recyclability, HPDCABSTRACT - Magnesium is the 8th most abundant element in the earth’s crust and itsextraction is done by Electrolytic process and Thermal reduction. These processes are costly(technically and economically). It has good properties: the lightest of all structural metals,conserves weight without sacrificing strength and rigidity which can be an alternative materialfor inner components as seats, window regulators or steering wheels in order to reduce theweight and therefore saving fuel consumption (CO2 emissions). Another important property isits recyclability. Mg is very reactive, that is why it can be alloyed (Al, Zn, Rare earths, Be),and receive surface treatments as the electrochemical one. The most common manufacturingprocess is High Pressure Die-Casting. In general there are three main types of HPDC alloys:The AZ91 which exhibits good combination of strength, ductibility and castability. TheAM60 and AM50 for high energy absorption applications, and the ones used for high temp.Applications such as the AE42 and AS31 (powertrain at temperatures up to 150ºC and200ºC). The alloys are produced in ingot form. Finally, thanks to its attractive characteristicssome pioneering companies in Europe are starting to integrate it in its products.TECHNICAL PAPER – History until 1945, Joseph Black (1755), Scottish chemist,discovered that magnesia contained a new element: magnesium. In 1808, Sir Humphrey Davyisolated the metal. Magnesium found steady interest only in Germany which was the onlyproducer in the world, using the metal mostly as powder or ribbon for flashlights and otherpyrotechnical purposes. The first Beetle car whose weight contained 20 Kg of this metal wasdesigned by Porsche engineering. Since 1945, In Europe, production of magnesium decreaseddrastically. At the same time, countries like America or Asia, were improving the process toobtain pure magnesium metal and increased the production of magnesium and alloys to use itin other tools like Civilian user: Cars, Kitchen furniture, Aircraft, Cell batteries, etc..PRODUCTION TECHNOLOGIES OF MAGNESIUMMagnesium is the eighth most abundant element on Earth and constitutes about 2% of theEarth’s crust. It is the third most plentiful element dissolved in seawater and it can be found inover 60 minerals. There are six sources of raw materials for the production of magnesium: 1. Magnesite (28.8% weight of Mg) [ MgCO3 ] 2. Dolomite (28.8% w.o. Mg) [ MgCO3*CaCO3 ] 3. Bischofite (11.96% w.o. Mg) [ MgCl2 * 6H2O ] 4. Carnallite (8.75% w.o. Mg) [ MgCl2 * KCl * 6H2O ] 5. Serpentine (26.36% w.o. Mg) [ 3MgO * 2SiO * 2H2O ] 6. Olivine (33% w.o. Mg) [ (Mg, Fe)2SiO4 ] 7. Sea water (0.038% - 20.8% w.o. Mg) [ Mg2+(aq) ]Magnesium always appears in nature bivalent ionic form. Mg2+ + 2e- = Mg [E0 = -2.375 V] (1) 1
  2. 2. In 2006, production of primary magnesium in the world was approximately 726.000 metrictons. As shown in figure 1, evolution of production per year by continent. Production of primary Magnesium in XXI century 800 700 ASIA 600 AMERICA EUROPE Metric Tons 500 400 300 200 100 0 2000 2001 2002 2003 2004 2005 2006 Years Figure 1: Statistics of Magnesium production from IMAOn the one hand, all the “Electrochemical technologies” use direct current electricity form,which passes through the electrolysis cells and discharges chlorine and magnesium ions intogaseous chlorine and metallic magnesium. The basic raw materials for the production ofmagnesium with this process are generally divided into two: salts containing chloride and rawmaterials that must be transformed into salts containing chloride. Eventually, all the materialswill become either Bischofite or Carnallite prior to drying and feeding into the electrolysiscells.On the other hand, the “Thermal Reduction” methods are based on heating of magnesia in thepresence of various reduction materials, to a variety temperatures. The only ores used in theproduction of magnesium are Dolomite and Magnesite. The ores are extracted throughtraditional mining methods, mainly through open mining. The ore extracted from the mineundergoes calcinations at temperatures of 700-1000ºC.Advantages and disadvantages of the different processes Thermal Comparative parameter Electrolytic technology reduction technology Magnesite, Dolomite, Magnesite, Raw materials Bischofite, Carnallite, Dolomite Serpentine, Sea water Energy Sources Hydro power, Gas, Fuel Coal, GasEnergy consumption per ton of Mg [ Mw / h ] 18-28 45-80 Capital investment per ton of Mg [ € ] 7000-12000 Up to 1300 Operational conditions Continuous process Batch Process Operational Man Power X Up to 5X Table 1: Comparison between electrolytic and thermal reduction processes 2
  3. 3. PROPERTIES PURE OF MAGNESIUM Property Conditions Measure Comment Classified Alkaline earth metal Crystal Structure hcp Density [ gr/cm3 ] 20ºC 1,738 ++ ( Lightest structural material) Coif. of linear thermal expansion 20ºC-100ºC 26,1 x 10(-6) ++ “αT” of polycrystalline ( /ºC) 20ºC-500ºC 29,9 x 10(-6) Youngs modulus of elasticity (Gpa) 20ºC 44 = Module of stiffness (Gpa) 20ºC 17 - Melting Point (ºC) 650 + Boiling Point (ºC) 1107 + Coefficient thermal conductivity 0ºC 155,3 ++ (W/mK) 423ºC 154,1 Reactive High -- Castability Manufacturing Good ++ Ductibility Table 2: Properties of Magnesium; (++) = Very good, (+) = Good; (=) =equal; (-) = poor; (--) = Very poorAnother property is damping capacity, the ability to dissipate elastic energy. There are twomain types of damping: anelastic and hysteretic. High damping capacity will only reducevibrations that cause anelastic strains in the part body. In general, all Mg-alloys can be tunedto those critical frequencies where noise, vibration and harshness (NVH) are reduced.Magnesium parts have excellent damping capacity in spite of damping depends on manyfactors, e.g. purity, grain size, alloy composition, amplitude, temperature and frequency. TheMg-alloys have a damping average value, measured with “The loss factor” of 0.004. It can beintroduced another subject “Squeaks & rattles”, because the possibility of magnesium like“package bodies” reduces the assembly parts.DESIGNATION OF MAGNESIUM ALLOYSMagnesium, like other structural metals, must be alloyed with other metals to be employed forengineer applications. The ASTM employs the following system:Ex: AM60a A (alpha): Primary alloying element designation M (alpha): Secondary alloying element designation 6 (numeric): Primary alloying element nominal wt% (from 5, 5% to 6,5%) 0 (numeric): Secondary alloying element nominal wt% (from 0% to 0, 5%) a (alpha): RevisionAlloying elements designations:A- Aluminium; E- rare Earths; J- Strontium; K- Zirconium; M-Manganese; S-Silicon;X- Calcium; Z-Zinc.Main types of Magnesium alloys: 1. Conventional: AZ91D, AM60B, AM50, AM20 2. Creep resistant: AS31, RE-alloys, Ca-alloys, Sr-alloys 3
  4. 4. 3. New alloys: AM-lite, HyMag 1, HyMag 2, MRI 153M, MRI 230D 4. Other: AS21, AS21X, AS41MANUFACTURINGMg-alloy component can be manufactured by all the conventional techniques includingcasting, forging, extruding and rolling. Figure 2: Type of manufacturing of Mg-alloysAccording to the figure 2, there are so many types of manufacturing Mg, but the mostcommon Mg-alloy components are produced via High Pressure Die Casting (HPDC) whoseprocess has two ways, either “Hot chamber” and “Cold chamber”. Hot chamber [H.C.] Cold Chamber [C.C]The injection system is dipped in molten Speeds and pressures are higher can be obtainedmetal majors.Shorter Cycles More compact pieceNecessity to fuse fine thicknesses Majors investmentsHigh limitations in the design of the pieces. Major Probably oxidation of the materialProcess limited a few magnesium alloys There are only alloys that can be injected in C.C. Greater possibilities in designing pieces Table 3: Properties between different chambers in HPDC Figure 3a: Hot Chamber Figure 3b: Cold ChamberHPDC is by far the most common production method accounting for 70% of the magnesiumused and it is growing in excess of 15% per year thanks to automotive applications.The main in die casters in Europe are: Grupo Antolin Magnesio, Dynacast, HDO, GeorgeFisher Mossner, ECKA Granulate GmbH, Magna Steyr, Dead Sea Magnesium, MagnesiumElektron, Gjutal, Tonsberg, Meridian, Zitzmann Druckgrass,… 4
  5. 5. Traditionally the Workhorse alloy has been Mg-Al and most of the alloys used are typesAZ91 because it shows superior castability and good mechanical properties, combined withgood corrosion resistance for the high purity versions of the alloy. Introduction of the high-ductility, energy absorbing alloys in the AM-series is a major driving force behind theexpansion of the automotive use of magnesium die-casting. These last alloys are used forcomponents like steering wheels, seats, doors, body parts… that are subjected to deformationduring a crash. Table 4 shows the main factors which can to be considered to alloy elements: Room temperature mechanical properties of die casting alloys Elements Yield Tensile Elongation Hardness Al Mn Zn Other Strength Strength Types [ N/mm2 ] [ N/mm2 ] [%] [ HB ] AZ91 9,00% 0,13% 0,70% 160 250,00 7,00 70,00 AM20 2,10% 0,10% 90 210,00 20,00 45,00 AM50 4,90% 0,26% 125 230,00 15,00 60,00 AM60 6,00% 0,13% 130 240,00 13,00 65,00 AE42 4,00% 0,10% 2,5% RE 145 230,00 11,00 60,00 AS41 4,20% 0,20% 1% Si 140 240,00 15,00 60,00 Table 4: Comparison between different mechanical properties of Mg-alloysMANUFACTURING PRODUCT DESIGNThe main demands on potential Magnesium components affect four vehicle modules: drivetrain, interior, body and chassis. Magnesium can improve vehicle design and add uniquecustomer feature. One of the reasons why Mg could be an alternative in body design is as“element housing”. In addition, Components consolidation eliminates expensive assemblyoperations.The following Basic design guidelines should give a first help in designing magnesium Highpressure die cast structure [HPDCs]: 1. Specify thin sections which can easily be die cast and still provide adequate strength and stiffness (wall thickness from 0.5 to 10mm). 2. Keep sections as uniform as possible 3. Keep shapes simple and avoid stress concentration 4. A slight crown is more desirable than a large flat surface. 5. Specify coring for holes or recesses where we can save in metal and overall costs outweigh tooling costs. 6. Avoid small cores (cored holes diameter should be more than 2mm). 7. Provide sufficient draft on side walls and cores to allow easy removal of the die casting (average 2º). 8. Appropriate corner design (Radii should be more than thickness of fillets). 9. Cast-in inserts should be designed to be held firmly in place with proper anchorage provided to retain them in the die casting. 10. Design parts to minimise flash removal costs 11. Never specify dimensional tolerance closer than essential (increases costs) 12. Where machining is specified, allow sufficient metal (nominal size + tolerance + 0.2mm) for required cuts and consider the draft angles. 5
  6. 6. Magnesium applicationsMg-alloys are very attractive in applications for the automotive, railway and aerospaceindustries as shown figure 4 and figure 5. Figure 4: Seat, safety test by Grupo Antolin, Spain Figure 5: Seat of Mg-alloy [AM60] casting by Grupo Antolin magnesio, SpainPOST-MANUFACTURING (SURFACE FINISHING)Commonly what is done with the Post-manufacturing in Mg-alloys is to improve corrosionresistance, maintaining a good surface appearance (low roughness), at least in parts of currentseries. According to the experience in automotive area, terms of a good coating could be:Measure thickness (30-45 microns), good adhesion, good finish roughness, Ra <1 micron,resistance to atmospheric corrosion, Galvanic resistance, Filiform corrosion resistance(scratch resistance), Coatings free of chromium and Cheap (the automotive sector workingwith small margins).CorrosionMagnesium alloys have had a poor reputation for corrosion lower resistance for manydecades, particularly in salt-water environments. There are so many factors involved tocorrosion, in essential, we can found two types of cause of corrosion: external factors (whichinclude the humidity, content and type of salt ions in water, temperature and assemblypractices”Galvanic attack”) and internal factors (which included the alloys composition,purity of Mg, contaminants, the fabricated form: die-casting, microstructure and surfacequality). 6
  7. 7. Figure 6: Factors influencing the corrosion properties of Mg-AlloysGalvanic Corrosion (GC)GC occurs when magnesium is connected to other metallic materials in the presence of anelectrolyte. Figure 7 shows the basis for galvanic corrosion for the case of bolting twomagnesium castings together. The anode (corroding metal) and cathode (noble metal)reactions must balance each other, which mean that by reducing the consumption of electronsin the cathode reaction, the production of electrons in the anode reaction is reducedaccordingly. Figure 7: Basis for galvanic corrosionThe key factor is the selection of the cathode material. Such materials are much morecompatible with magnesium. Table 5 gives an overview of compatible and non-compatiblematerials. Compatible material Non-compatible material Aluminium 5xxx and 6xxx series Steel and stainless steel Tin Copper Zinc Nickel Plastics and polymers Titanium Selected aluminium alloys ( 2xxx and A380) Table 5: Compatible and non-compatible materials with magnesium die castingPrinciples and prerequisites for Optimum Surface ProtectionIn order to achieve the optimum surface protection for the Mg-based material, the followingprinciples, prerequisites and recommendations should be observed in table 6: 7
  8. 8. Smoothing by polishing, honing, grinding or Methods of pre- Mechanical blasting treatment of the metal Use of organic solvents and/or alkaline surface Cleaning cleaning agents Electroless Electrochemical Physical methods treatment treatment Anodisation ( DOW 17, Chromating PVD HAE, ANOMAG)Methods of applying Anodical plasmachemical Chromiumfree Flame or plasmainorganic coatings treatment (ASD) systems spraying on the Mg surface (MAGOXID, TAGNITE) Electroless nickel Electroplating (Zn, Cu, Laser or electro Ni, Cr, etc..) beam treatment Painting Water paints Methods of applying organic Powder paints / EPScoatings on the Mg surface or on Structural paints the inorganic undercoating Immersion paints Anti friction paints Table 6: Surface treatment of magnesium based materialsRECYCLINGEnvironmentally respectful and cost effective use of Mg-alloys in automotive applicationsassumes efficient closed loop recycling of die casting returns and post-consumer scrap. Thesetwo recycling processes are issues capable of regaining the original chemical composition andcleanliness of the Mg-alloys. The energy requirement for melting and recycling Mg is onlyabout 5% of the energy to produce the same quantity of primary material. Traditionally,recycling by melting with flux has been used, but over the last decade, flux-free solutionshave emerged, partly linked to in-house recycling in die casting shops. While the industrytoday effectively recycles the clean process scrap (class 1) in closed loop, the challenge in theshort term is to close the loop for the lower grade scrap such as droop and chips.The classification system applied by “Hydro Magnesium” divides the scrap into the followingclasses:Sorted clean returns (trimming casting defects) [Class 1], Sorted clean returns with insert(Other returns) [C2], Sorted oily/painted returns (Other returns) [C3], Sorted dry chips(Machining) [C4], Sorted oily/wet chips (Machining) [C5], Dross – salt –free (Melt loss) [C6], Sludge- with salt [C7], Mixed and off-grade returns (Other returns) [C8].Regardless of class, except for ELV scrap, recycling of Mg will follow a general route: Figure 8: General process steps for Mg-alloy recycling 8
  9. 9. CONCLUSION, AUTOMOTIVE APPLICATIONEnvironmental conservation is one of the principal reasons for the focus of attention onmagnesium to provide vehicle weight reduction, CO2 emission and fuel economy.Improvements in Mg alloying and processing techniques will make it possible for theautomotive industry to manufacture lighter, more environmentally friendly, safer and cheapercars. The dramatic benefit that reduced automobile weight can give in terms of improved fuelconsumption is showed in figure 9. FUEL ECONOMY Vs AUTOMOBILE WEIGHT 30,00 FUEL ECONOMY [ Km / litre ] 25,00 20,00 15,00 10,00 5,00 - 54,00 450 908,00 1100 1.362,00 1.816,00 2.300,00 2.770,00 VEHICLE WEIGHT [ Kg ] Figure 9: Fuel economy versus vehicle weightACKNOWLEDGEMENT - The author would like to express his acknowledgment to GrupoAntolin company: Mr. Diego Val Andrés (Magnesium Technique), Ms. Rosalia ArribasFernandez (Marketing), Mr. Abel Dionisio Rodriguez Tejido (Simulation & test), Mr. OscarCalvo Herrera (Simulation & test), Mr. Mariano Cabrerizo Juarez (Acoustic & Vibration),Mr. Jose Luis Pascual García (Acoustic & Vibration), Mr. Rafael García García (AdvancedSystem Engineer) and Mr. Francisco Javier Martinez Moral (Chief R&D) for theirs supportand suggestions. Finally, this work was supported by Grupo Antolin Company.REFERENCES(1) Horst E. Friedrich, Barry L. Mordike, “Magnesium Technology: Metallurgy, Design data, Applications”, Ed. Springer, ISBN-10 3-540-20599-3, 2006.(2) Grupo Antolin Company, “White book of magnesium”, 1999.(3) International Magnesium Association (IMA), www.intlmag.org(4) D.Eliezer, E.Aghion, F.H.( SAM) Froes, “Magnesium Science, Technology and Applications”, 1998.(5) Mustafa Kemal Kulekci, “Magnesium and its alloys applications in automotive industry”, DOI 10.1007/s00170-007-1279-2, 2007(6) Hydro Magnesium, Technical Brochure. 9