VIBRATING METAL MELTS SOLUTION COMPACTION WALL CASTINGS

Transcription

1 VIBRATING METAL MELTS SOLUTION COMPACTION WALL CASTINGS I. MĂRGINEAN, B. FLOREA, B.Al. VERDEŞ UNIVERSITY POLITEHNICA BUCHAREST ABSTRACT: Compacting casted pats and educing the bliste on the solidification of alloys ae equally inteests in impoving the quality, chaacteistics and educing manufactuing costs by inceasing the emoval esult index fom bliste compaction. Theoetical and expeimental eseach conducted by the authos has lead to obtain beneficial esults in this espect. This pape pesents the esults and conclusions dawn fom this eseach. 1. INTRODUCTION The stuctue and physical-mechanical chaacteistics of a casted metal mateial ae influenced by its density and compactness. At the alloys solidification it can occu discontinuities, due to the shinkage phenomenon, chaacteistic of most alloys and to the ponounced decease in solubility of gases in the melt, at cystallization tempeatue. 2. THE STUDY Obtaining a compact metal mateial is povided if the v speed of the alloy penetation into capillay channels of the biphasic zone is equal to the contaction speed v cont. v cont = α mr [m/s] (1) whee: α - contaction coefficient of the alloy at solidification; m - atio between the liquid mass volume fom the biphasic zone and this zone s volume; R - ate of occuence of solid phase [m/s]. In odinay conditions, the v speed is expessed as such: 2 Pe + Pm Pg + cos θ v =, [m/s] (2) 8η l whee: - adius of the capillay channel [m]; P e extenal pessue [Pa]; P m metalostatic pessue [Pa]; P g channel gases pessue [Pa]; σ - supeficial tension of the alloy [N/m]; θ - wetting angle [ad]; η - dynamic viscosity of the alloy [Pa s]; l - length of penetation of the alloy in capillay channels [m]. Fom the equality of the two speeds v=v cont esults: 2 Pe + Pm Pg + cosθ = α m R (3) 8η l fom whee: 2 Pe + Pm Pg + cosθ l = (4) 8ηα m R Mechanical oscillations deceases the supeficial tension σ at the liquid-solid inteface wetting angle θ and impints the alloy a maximum initial speed v i = Aω. Mechanical vibations action poduces in the biphasic zone a dendite fagmentation, 915

2 educing the length of capillay channels to be coveed by the liquid alloy to fill the gaps caused by shinkage and incease the speed of the liquid alloy flow in these aeas, impoving supply conditions in mico-cavities. Also, vibations detemine a maco-bliste concentation and a eduction of the poosity in the hot spots, an effect explained by inceasing the melt flow. Mechanical vibations applied in liquid metal alloys intoduce new foces that detemine changes in the macostuctue and macobliste of the casted pats. The size, shape and position of mico-bliste can be detemined theoetically by plotting isothems of solidification in the walls of the casted pats. Maco-bliste is located in those aeas of the wall whee the liquid alloy solidifies last and alone. Maco-bliste consists of one o moe concentated cavities in clealy defined aeas, they esult fom the solidification of lage volumes of liquid alloy. Maco-blistes ae called as well concentated blistes. The alloy layes that isolate the blistes between them and cove them in the top pat ae called decks. The main maco-bliste is found in the uppe pat to the casted pat compaed with the casting position, while the seconday macobliste is found in the lowe pat o in hot spots in the themal axis zone. Maco-bliste is detemined using technological evidence, while mico-bliste by applying methods of flaw (X o gamma ays) o by detemining the density of samples cut fom the casted pat wall. The volume, shape and position of the macobliste and mico-bliste in the walls of the casted pats ae influenced by seveal factos which at thei tun depend on the technological natue of the alloy, the natue of the mold, the casting conditions and the casted pat geomety. The total volume of the bliste is: V = V MR + V m (5) in which: V MR - the maco-bliste volume; V m - mico-bliste volume. The factos which influence the bliste ae the following: - alloy s natue; - fom s natue; - casted pat geomety; - casting conditions. Avoiding the pocess of developing a micobliste is impossible, but the outing of the contaction pocess in ode to obtain a macobliste with as smalle as possible volume and with an optimum distibution in the pat s wall is possible. 3. ANALISES, DISCUSIONS, APPROACHES and INTERPRETATIONS The development of the alloy was made in a cucible funace, heated by buning a natual gas flame. Afte melting, the tempeatue was inceased and maintained at C. Fo casting and solidification of the samples wee used metal foms. Fig 1. Alloy s solidification Fig. 2 Extaction of vibated samples fom the mold Among physical popeties, density is diectly elated to the development pocess and epesent the unit volume s mass. Fom the pefomed measuements pefomed we can emembe the following: sample casted fom non-vibated alloy, solidified in outdoo ai; (O) 916

3 sample casted in non-vibated alloy, solidified unde the influence of vibation afte casting until solidification; (V) sample casted fom alloy vibated in pot, solidified without vibation (O ) sample casted fom alloy vibated in pot, solidified unde the influence of vibation afte casting until solidification. (VV) a b Fig. 3 Bliste aspect fo diffeent situations a- non-vibated; b- the vibation of melted alloy (only in pot, befoe casting) a b Fig. 4 Examples of section blistes a- solidified unde the influence of vibation afte casting until solidification; b- vibating the alloy in the pot and duing casting until solidification. Vibations detemine maco-bliste concentation, a decease of poosity fom the liquid alloy, to manage the fomation pocesses and stuctue compacting with small cystals which pesent the best physical and mechanical chaacteistics, including inceased density of casted alloys with those advantages. Measuement esults ae pesented in Table 2 fo an aluminum alloy type ATSi12.5 Mg0.25. Table 2. The measuements esults on non-vibated, vibated samples No. Sample Sample mass [g] Volume [cm 3 ] Density [g/cm 3 ] 1 O 30, ,6 2,66-2 V 31, ,4 2,79 4,88 3 VV 30, ,9 2,83 6,39 Mechanical popeties ae also detemined by the macostuctue because of the existence of chemical heteogeneity, cystalline o mechanical o discontinuities that play the ole 917 Density incease thought vibating [ % ] of powe and mico-concentatos, by size, cystal fom, natue and mophology of stuctual constituents. Table 3 shows the values obtained by caying out systematic evidence of esistance to

4 factue, yield, and elongation at beak fo the fou types of casting: - casting in gavitational field (O); - casting afte the liquid alloy vibating in the mold (O ); - vibating afte casting in the mold until solidification (V); - sample fom the liquid alloy vibated in the pot casted in the mold and vibated until solidification (VV). Table 3. Values fo tensile stength, yield, elongation, weakening the factue toughness fo the cast alloy AlSi12.5Mg0.25 of samples ealized duing eseach. No. Sample R m R p0,2 A u Z HB Obsevations type [MPa] [MPa] [%] [%] [MPa] R1 O , Un-woked sample R2 O ,04 88,6 The split inclusions 0.5 mm R3 O ,2 2,2 87,3 R4 O / ,2 5,8 89,3 Un-woked sample inclusions in the aea fom feede R5 O / 2 93, Defect in stuctue, bliste with a diamete of 1.5 mm R6 O / ,6 R7 V , R8 V ,7 104,3 R9 V ,9 2,7 106,3 R10 V ,9-103,1 R11 V ,2 R12 VV Defect in stuctue R13 VV ,6 3 99,3 R14 VV ,2 1,5 98,6 R15 VV ,1 2,1 97,2 R16 VV ,8 97,3 Tuning diamete of 50 mm, sample in the themal axis mateial compaction, evidenced by inceasing the hadness by about 5 pecent compaed with the goss alloy. Following eseach which efes to teating metal melts with mechanical vibations, highlighting the fact that they have positively influenced the stuctue obtained afte solidification and on mechanical popeties, in the sense that it impoves them. The values obtained ae much highe than those obtained in the classical vaiant. The mechanisms by which these vibations act on the liquid phase duing solidification and melting ae complex. Explanation and undestanding of these mechanisms is of geat theoetical and especially pactical impotance, allowing us to define appopiate technology fo teatment of melt with vibations. Figue 5 shows the vaiation of the degassed alloy hadness unde the influence of vibation (50Hz) in the casting pot. It is noted that thought gas elimination was achieved a Hadness MPa HARDNESS Seies Distance mm Fig. 5 HB-hadness vaiation on the adius fo alloy AlSiMg vibating pot, gavitational casting fo the φ 20mm disc, sample O 2 918

5 4. CONCLUSIONS The contou analysis of the contaction gap leads to the conclusion that unde the natual action of vibation is educed the bliste depth and its lowe pat is ounded. Fo the alloys with high contaction, pone to cacking, it was obseved that due to mechanical vibations the mico-blistes decease educing axial poosity. Unde the influence of mechanical vibation deceases the total volume of maco-bliste and focuses on the supeio side, educing the volume of liquid alloy fo feedes. The main favoable technological effects obtained by applying physical-mechanical teatments, consisting of inceasing compactness and impoving the stuctue of castes pats. It also finds a shap incease in hadness values by 25 pecent compaed to a gavity cast alloy (static), a slight decease in the hadness towads the themal axe, at the same diametes o diffeent diametes of the samples a longe vibating time leads to chopped micostuctues and highe hadness values. 5. REFERENCES 1. BAUM B.A., TIAGUNOV G. B. - Potessa litiia, Moskova CĂMUI C. - Studii şi cecetăi pivind efectul acţiunilo fizice ale enegiei vibaţiilo de joasă fecvenţă asupa cupului în momentul tunăii şi solidificăii în semifabicate; lucae de absolvie cusuii post univesitae, Bucueşti MĂRGINEAN I., VELICU Şt. - Pocedee speciale şi neconvenţionale în tunătoii, vol. I şi II. Ed. BREN, Bucueşti PÂRVULESCU C.-Cecetăi pivind influenţa vibăii asupa solidificăii aliajelo tunate în piese; Teză de doctoat, UPB POP M.A.-Cecetăi asupa tehnologiilo şi mateialelo modene pentu confecţionaea ganituilo de model; Teza de doctoat, UT Başov ŞUŞU C.-Contibuţii la îmbunătăţiea calităţii topituilo uno aliaje de aluminiu destinate tunăii pieselo; Teză de doctoat, UT Cluj-Napoca