PROGRESS IN DUCTILE ALUMINIUM HIGH PRESSURE DIE CASTING ALLOYS FOR THE AUTOMOTIVE INDUSTRY

Memorie >> Die csting PROGRESS IN DUCTILE ALUMINIUM HIGH PRESSURE DIE CASTING ALLOYS FOR THE AUTOMOTIVE INDUSTRY R. Frnke, D. Drgulin, A. Zovi, F. Csrotto Tody the die csting process is used to cst prts with high qulity requirements such s engine crdles, cross memers nd nodes for spce frme construction. This hs presented the chllenge to design lloys with superior mechnicl properties. For crsh relevnt prts requiring high ductility (elongtion > 12 %) one option to meet these properties is y het treting low iron Al-Si lloy to T4 or T7 temper. However het tretment cn led to prt distortion nd listering resulting in higher costs for the producer. The second option is Al-Mg lloys type which fulfill these requirements in the s-cst stte ut the lloys re not esy to cst. Reserch ws strted using the esy to cst Al-Si lloy system trgeting high elongtion (> 12 %) nd yield-strength (> 120 MP) lredy in temper F nd not showing ny long term ging ehvior. This pper will discuss the technicl progress which egn in the erly 1990ies, gining in importnce with the first series spce frme Aluminum cr, continuing with structurl prts pplied in the s-cst stte nd pproching future with n incresing mount of light weight components replcing steel nd het treted Aluminum designs. PAROLE CHIAVE: light-pressure die csting lloys, ductility in the s-cst stte, utomotive, ductile l-lloys INTRODUCTION The utomotive industry hs provided the driving force for the development nd production of new die csting lloys. From technicl point of view the field of ppliction for stndrd luminium lloys is limited. These lloys re minly used for prts with simple requirement profile, usully low weight nd certin yield strength. The qulittive evlution in Fig. 1 shows the limits of stndrd lloys. An Al Si9Cu3-type (226) is minly used for prts without ny requirements concerning ductility or good resistnce to corrosion. An Al Si12-lloy provides certin ductility when cst into permnent mould ut hs no remrkle yield strength. Somewhere in etween other compromises my e found. Aluminium Rheinfelden presented Silfont -36 for the first time in 1994 s the first ductile luminium lloy for highpressure die-csting. The chemicl composition is shown in T. I. Silfont -36 is sed on the luminium-silicon system with its known good csting ilities for high-pressure die-csting. The mngnese content is kept in rnge of 0,5 to 0,8% SILAFONT -36 Rüdiger Frnke, Dn Drgulin, Ann Zovi, Federico Csrotto Aluminium Rheinfelden GmH, Germny Fig. 1 Rnking of luminium lloys focussing on the mechnicl properties. Clssificzione delle leghe d lluminio stndrd e di quelle mrchio Rheinfelden sull se delle loro crtteristiche meccniche. l metllurgi itlin >> mggio 2007 21

Die csting << Memorie Fig. 2 : Al Si10Mg stndrd mteril, smple thickness 4 mm, no Sr modifiction, 5% elongtion in temper F : Silfont - 36, smple thickness 4 mm, Sr-modified, 10 % elongtion in temper F. : Un leg Al Si10Mg stndrd. Spessore di prete di 4 mm, non modifict llo Sr, 5% di llungmento llo stto grezzo F. : Silfont -36, spessore di prete di 4 mm, modifict llo Sr, 10 % di llungmento llo stto grezzo F. weight percent. Below the cst prt my stick to the die, ove the elongtion my suffer from the growing mngnese phses. Mgnesium is dded for the yield strength. Low Mg-contents mke ductile lloy with lower yield strength, wheres high contents ring up the yield strength nd decrese the elongtion. Titnium hs the typicl grin refining effect nd increses cstility nd mechnicl properties. 100 to 200 ppm strontium re dded to modify the eutectic. Fig. 2 shows the microstructures of not modified eutectic on the left nd Srmodified eutectic on the right hnd side. The modified eutectic is considerly finer which hs positive influence on the elongtion. Bsed on the mechnicl properties in temper F, s result of the chemicl composition nd the microstructure chieved y metllurgicl mens, Silfont -36 offers wide vriety of mechnicl properties ccording to the het tretment nd the Mgnesium content (see Fig. 3). For Fig. 3 Mechnicl properties of Silfont -36 for different het tretments. Crtteristiche meccniche di Silfont -36, in funzione del contenuto di mgnesio e del trttmento termico. pplictions requiring high ductility T4 (solution tretment, quenching & nturl geing for t lest six dys) or T7 (solution tretment, quenching & overgeing) temper re recommended. For high yield strength T5 (quenching fter ejection & rtificil geing) or T6 (solution tretment, quenching & rtificil geing) temper my e dequte. SOME APPLICATIONS IN SILAFONT -36 The first mjor ppliction for Silfont -36 were nodes produced in high-pressure die csting for spce frme construction of n upper clss pssenger cr. The min requirements were medium yield strength, weldility, corrosion resistnce nd most of ll ductility. Tody Silfont -36 my e considered s n lloy known ll over the world. A more recent ppliction is shown in Fig. 4. Here we cn see the engine crdle of high volume middle min mx Si 1,8 2,6 Fe 0,2 Cu 0,05 Mn 0,5 0,8 Mg 5,0 6,0 Zn 0,07 Ti 0,20 Be 0,004 Others 0,2 T. 1 Chemicl composition of Mgsiml -59 in weight-%. L composizione chimic di Mgsiml -59 in peso %. min mx Si 8,5 10,5 Fe 0,15 Cu 0,05 Mn 0,35 0,60 Mg 0,06 Zn 0,07 Ti 0,15 Sr 0,006 0,025 Others 0,2 T. 2 Chemicl composition of Cstsil -37 in weight-%. L composizione di Cstsil -37 in peso %. 22 mggio 2007 << l metllurgi itlin

Memorie >> Die csting Fig. 4 Engine crdle for middle nd upper clss pssenger cr. Supporto motore di un uto di ctegori medio-lt. clss cr in temper O. A similr prt is used in luxury cr in temper T6. The ssemly sitution on the right hnd side with the surrounding front suspension shows clerly tht this prt hs to provide good deformility in cse of crsh nd certin yield strength in order to crry the engine (not shown) mounted onto the crdle. The mechnicl properties re enhnced y upgrding the die csting process with vcuum system. The necessry rigidity is provided y ris tht cn e seen in the lower prt of the csting. Although exposed to hevily corrosive conditions the crdle does not require ny surfce protection. It mesures 0,92 m y 0,17 m y 0,17 m nd weighs 10,2 kg. Fig. 5 Mechnicl properties of Mgsiml -59 s function of the wll thickness. Le proprietà meccniche di Mgsiml -59, in funzione dello spessore di prete. MAGSIMAL -59 In 1996 n lloy ws presented to the mrket, which ws unusul for high-pressure die csting t tht time: the AlMgSi-type Mgsiml -59. So fr this type of lloy type hd een minly used for permnent mould csting nd ws especilly known for its excellent resistnce to corrosion even in se wter. However in ddition to tht it offers further properties nd ilities when used in high-pressure die csting which mke it superior to mny other lloys. In T. 1 the chemicl composition is shown. Other thn most lloys for high pressure die-csting Mgsiml -59 contins five to six percent Mgnesium nd roughly two percent of Silicon. A surplus of Mgnesium nd low Copper nd Zinc contents mintin the excellent resistnce to corrosion. Iron is kept low to keep up the elongtion. Beryllium is dded to reduce dross during the melting process. Together with quick solidifiction very fine microstructure consisting of n -solid solution nd 40% Mg2Si-eutectic is creted with superior mechnicl nd ftigue properties in temper F. As the fineness of the microstructure depends on the solidifiction velocity, the geometry of the csting hs n influence on the mechnicl properties. The influence of the wll thickness on the mechnicl properties is shown in Fig. 5. The thinner the wll thickness is, the higher oth yield strength nd elongtion re ecuse the microstructure ecomes finer. For the designing engineer this ehviour of incresing properties with decresing wll thicknesses hs dvntges, ecuse thin nd light design promotes the performnce of the mteril. However some recommendtions looking t the complexity of the design hve to e tken into ccount due to the higher shrinkge of this lloy type. The die design requires lrger rdiuses nd drfts Fig. 6 Shock tower of the new upper middle clss cr ) csting in Mgsiml -59, ) front structure in Aluminium during ssemly. Duomo dell sospensione di un nuov uto di clsse medio-lt. ) getto in Mgsiml -59, ) prte frontle del telio durnte l ssemlggio. l metllurgi itlin >> mggio 2007 23

Die csting << Memorie Fig. 8 Mechnicl properties of Cstsil -37 in temper F. Crtteristiche meccniche di Cstsil -37 llo stto grezzo. hs to resist the sttic lod from the cr weight nd the dynmic shocks coming from the suspension. The prt is designed with thin wll thicknesses to receive the required yield strength nd t the sme time providing high elongtion for good crsh ehviour. The cst prt is connected to the surrounding profiles nd wrought Aluminium prts y gluing, selfpierce-riveting nd MIG-welding. Due to the excellent corrosion resistnce the prt does not require pint coting. CASTASIL -37 Fig. 7 ) microstructure of n AlSi9Mg stndrd mteril, 3mm wll thickness ) Cstsil -37 microstructure, 3 mm wll thickness. ) Microstruttur di un leg AlSi9Mg stndrd. Spessore di 3 mm. ) Microstruttur di Cstsil -37. Spessore di prete di 3 mm. compred to n AlSi-type. None the less Mgsiml -59 with its excellent properties in temper F my sustitute pplictions in AlSi requiring het tretment cusing distortion nd strightening of the prts. SOME APPLICATIONS IN MAGSIMAL -59 Mgsiml -59 is n excellent mteril for die cstings, which hve to resist high sttic nd lternting lods nd provide good ductility t the sme time. Typicl pplictions re structurl nd suspension prts in pssenger crs. Fig. 6 shows the shock tower of n upper middle clss cr with completely new concept. With the gol to spred the weight of the vehicle evenly on front nd ck wheels, the front su-frme is entirely designed in Aluminium. The shock tower is structurl prt where the suspension strut is connected. So this prt With the development of Cstsil -37 Aluminium Rheinfelden is working on nother lloy for high pressure die csting pplictions in pssenger crs with complex designs requiring high ductility nd medium yield strength. These re for exmple nodes nd structurl components in spce frmes or su-frmes, usully with thin wll thicknesses nd complex nd rigid geometries. So fr these types of prts re minly cst in AlSiMg-type lloys nd solution het treted to receive the suiting properties. However solution het tretment cuses listering nd distortion of the prts, which hve to e strightened in n dditionl process step. Becuse of their complex designs these prts re difficult to cst in n AlMg-lloy. So the gol for the Cstsil -37 is to provide n esy to cst AlSi-lloy with t lest 12 % elongtion nd 120 MP yield strength in temper F. Since engine powers nd hence tempertures hve een going up during the pst yers n lloy is needed which shows no long term ging ehviour in high temperture environment. High resistnce to corrosion hs to e met y the wy. Cstsil -37 contins 8,5 to 10,5 percent silicon, which mkes the excellent cstility, typicl for this kind of lloy. Iron is kept low to mintin ductility, copper nd zinc likewise to prevent corrosion. Mngnese sustitutes iron nd voids sticking to the die. Strontium provides the known modifiction of the eutectic nd the linked ductility. Other thn most lloys so fr in this field of ppliction, Cstsil - 37 hs low mount of mgnesium. This mkes n even finer eutectic in ddition to the Sr-modifiction nd voids long term ging ehviour. In Fig. 7 the microstructures of stndrd mteril nd Cstsil -37 re shown for high pressure die cst 3 mm smple 24 mggio 2007 << l metllurgi itlin

Memorie >> Die csting pltes. In the microstructure of n AlSi9Mg stndrd mteril corse regions of the eutectic prevent the mteril from reching highest levels of elongtion in the s cst stte. These corse regions re due to mgnesium precipittions forming n Mg2Si phse. Without mgnesium this is voided nd the eutectic ppers even finer, s shown on the right hnd side. This mkes the dditionl step towrds higher elongtion in temper F. Looking t the mechnicl properties, shown in Fig. 8, slight influence of the wll thickness cn e stted. Here it ws exmined for wll thicknesses from 2 to 6 mm. The yield strength decreses with n incresing wll thickness. This is due to the slower solidifiction in lrger cross sections nd my e compensted y higher cooling of the die. The elongtion shows different ehviour. From 2 to three millimetres wll thickness it increses up to 14 percent in temper F where it remins up to 6 mm of wll thickness. The lower elongtion in thin wlls is proly due to the stronger impct of csting defects in smll cross section. SOME APPLICATIONS IN CASTASIL -37 Typicl cstings for Cstsil -37 hve complex designs nd require high ductility nd medium yield strength, good deformility, good resistnce to corrosion nd stle mechnicl properties when operting t elevted tempertures. In Fig. 9 the Spce-Frme nodes of the Lmorghini Gllrdo Spyder re shown. Die cst nodl points re decisive for specil rigidity in the ASF odywork of the open-top Spyder. The high yield strength of Cstsil-37 in the s-cst stte enled the very economic production of these weldle nodes. The minimum required elongtion ws of over 7% on the csting. With the use of Cstsil-37 weight reduction of out 10-15% in comprison with trditionl high-pressure die csting lloys ws possile. In ddition to this even etter Rigidity/Weight rtio s the steel one ws chieved. With mteril providing the desired properties in temper F or with single step het tretment strightening process ecomes osolete. c REFERENCES 1) Koch H., Hielscher U., Sternu H.; Frnke A. J., "Silfont -36, the new lowiron high-pressure die-csting lloy", TMS, Light Metls 1995, 1011-1018 2) Koch H., Hielscher U., Sternu H.; Frnke A. J.,"Mgsiml -59, n Al MgMnSi-Type Squeeze-Csting Alloy designed for temper F", TMS, Light Metls 1996, 933-937 Fig. 9 The high-pressure die cst nodes in Cstsil-37 for the ASF of the Lmorghini Gllrdo Spyder ) rer connection node ) internl A-pillr reinforcement c) folding-top struts. I nodi pressocolti in Cstsil-37 per l ASF dell Lmorghini Gllrdo Spyder ) nodo di connessione longherone posteriore ) rinforzo montnte nteriore c) ngolo superiore del prrezz. l metllurgi itlin >> mggio 2007 25

Die csting << Memorie A B S T R A C T CARATTERISTICHE DI ALLUNGAMENTO SUPERIORI NELLE LEGHE DI ALLUMINIO DA PRESSOCOLATA E LORO POSSIBILI APPLICAZIONI Keywords: lluminio e leghe, metlli, fonderi pressocolt Il processo di pressocolt moderno è clirto per ottenere getti dgli elevti stndrd qulittivi come supporti motore, trverse e nodi per strutture Spce-Frme. Quest sfid é il punto di prtenz per lo sviluppo di leghe dlle performnces meccniche superiori, con prticolr riferimento ll crtteristic di llungmento rottur. Diversi sono gli miti di ricerc per il rggiungimento di tli oiettivi prestzionli, prticolrmente importnti per il uon comportmento crsh: composizione chimic, trttmento termico e condizioni di solidificzione. Quest memori ripercorre le tppe dei progressi tecnici iniziti negli nni 90 e concretizztisi nell prim serie di utomoili struttur Spce-Frme. Più recentemente l ttenzione si è rivolt prti strutturli montte llo stto grezzo, per orientrsi poi verso componenti leggeri che sostituirnno sempre più spesso strutture in cciio o in lluminio trttto termicmente. ABBONATI ORA! Sri sempre ggiornto l meglio dl mensile d informzione più utorevole del settore metllurgico. Fondt nel 1909, si trtt dell prim rivist tecnic itlin sui metlli. Si distingue per l lto vlore tecnico-scientifico dei temi trttti reltivi ll ricerc, l produzione e gli impinti per l trsformzione dei mterili metllici; è in itlino con mpie sintesi in inglese. Riceveri comodmente dove preferisci i 10 numeri dell onmento, così non perderi nemmeno un occsione per trrre enefici dgli oltre 90 nni d esperienz l tuo servizio. SUBSCRIBE NOW! You ll e constntly kept up-to-dte y the most uthorittive puliction in the metllurgicl sector. Founded in 1909, it is the first Itlin technicl mgzine on metls. 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