Mohammad Anwar Karim Id :

Transcription

1 Department of Mechanical and Industrial Engineering ME 8109 Casting and Solidification of Materials EFFECTS OF RAPID SOLIDIFICATION ON MICROSTRUCTURE AND PROPERTIES OF AL, MG & TI ALLOYS Winter 2012 Presented by Mohammad Anwar Karim Id :

2 ORGANIZATION OF PRESENTATION Introduction Objectives and Methodology Overview of Rapid solidification Technology Rapid solidification effects on Al alloys Rapid solidification effects on Mg alloys Rapid solidification effects on Ti alloys Summary and Conclusion

3 INTRODUCTION Rapid solidification process is a technique- To solidify the melt of the material To employ the high cooling rate in excess of k/s during solidification To develop microstructure, mechanical and physical properties of the structure materials. It is important for the automotive, aerospace and plastic industries. As a low-density materials, lightweight metals like aluminum, magnesium, and titanium as prime candidates for structural applications.

4 OBJECTIVES AND METHODOLOGY Objectives To explore the basic concept of solidification behavior and rapid solidification (RS) process To recognize contemporary fields of application of rapid solidification technology Methodology Review from the books Review from the Journals Internet Browsing To summarize the effects of RS on microstructure & mechanical properties development of Al, Mg and Ti alloys

5 BENEFITS OF RAPID SOLIDIFICATION TECHNOLOGY Rapid solidification technology (RST) has been used To achieve unique microstructure To improve mechanical and physical properties To increase the range and quantity of alloying elements To refine grain size To enhance solid solubility To refine the segregation pattern To develop metastable phases To reduce dendrite arm spacing

6 EUTECTIC PHASE DIAGRAM

7 EUTECTIC PHASE DIAGRAM The minimum affects of nucleation behavior occur at lower cooling rate range K/s. At higher cooling rates, local equilibrium cannot be continued at the solid-liquid interface. Below the solidus line (below point 1), the melt will transform enormously to the α-phase of the same composition. Microstructural reformations in an alloy occur when content of the solute is higher than the maximum solid solubility Cmax.

8 EUTECTIC PHASE DIAGRAM From the equilibrium phase diagram, alloy composition C2 must contain a mixture of α and β phases At composition C3,there is an opportunity for the formation of metastable phases applying the undercooling produced by rapid solidification. Grain sizes of rapidly solidified materials are µm.

9 DENDRITE ARM SPACING VS COOLING RATE (DURING RAPID SOLIDIFICATION) As the cooling rate is increased from 0.01 to K/s, the dendrite arm spacing in different alloys is reduced from 100 µm to 1 µm.

10 CHARACTERISTICS OF ALUMINUM, MAGNESIUM AND TITANIUM Property units Mg Al Ti Atomic number Atomic weight g/mole Metallic valance Electronegativity Crystal structure h.c.p. f.c.c. h.c.p./ b.c.c. Nearest interatomic A distance Density g/cm³ Melting point C Normal electrode potential V

11 RANGES OF THE MAXIMUM EQUILIBRIUM SOLID SOLUBILITY S OF X IN AI-X, MG-X AND TI-X BINARIES System Type Solubility Range (at.%) < >25 AL-X E Be,Y,B,Re Acti, VIIIa, Ca Vb,VIb,Sr, Ba,Sn Be,Sc, Mn Si, Cu, Ge Ga, Li, Mg, Ag Zn (66.4) P Mo,Nb,Ta,W,Zr Cr,Hf,V,Ti M Bi,In,K,Na,Pb Tl,Cs Mg-X E As,Ba,Ce,Co Cu,Eu,Fe,Ge La,Na,Ni,Pd Pr,Sb,Si,Sr Au,Ca,Ir,Nd, Th Ag,Bi,Dy,Ga Gd,Hg,Pu,Sn Y,Yb,Zn,Zr AL,Er,Ho,Li Lu,Pb,TI.Tm P Mn,Ti Zr In,Sc I Cd(100) Ti-X BI V,Nb,Ta,Mo Eid Fe,Co,Ni,Cu Si,B Cr Pid B C Ge,Sn,O,H M-P Y,La,Ce,Nd Er,Gd Al,Ag

12 MAXIMUM EQUILIBRIUM SOLID SOLUBILITY OF ALUMINUM BINARY SYSTEMS Maximum elements form eutectic-type systems and have a maximum TSS which is greater than 1 %. Seven elements (beryllium, silicon, zinc, gallium, germanium, tin, and magnesium) form simple eutectic systems with aluminum. Outer transition metals belong to high melting points form peritectic type systems with Al with TSSs lower than 0.6 %. Other elements are partially miscible with Al and solidify monotectically with TSSs lower than.02 %.

13 MAXIMUM EQUILIBRIUM SOLID SOLUBILITY OF MAGNESIUM BINARY SYSTEMS Maximum elements form eutectic-type systems with Mg and have a maximum TSS which is greater than 1 %. for 20 elements. Only Five elements (indium, manganese, scandium, titanium, and zirconium) are recognized to form peritectic type systems with magnesium. Cadmium is only single isomorphous element which displays 100% TSS in magnesium.

14 MAXIMUM EQUILIBRIUM SOLID SOLUBILITY OF TITANIUM BINARY SYSTEMS Beta Stabilizers- Four elements form Beta Isomorphous systems with Titanium which has maximum TSS lower than 25% Six elements form Beta Eutectoid type systems with Titanium having maximum TSS 5 25 % Alpha Stabilizers Eight elements form Peritectoid type systems most of which have maximum TSS higher than 5 % Six elements form Peritectic type systems which have maximum TSS lower than 1%

15 EFFECT OF RAPID SOLIDIFICATION ON MICROSTRUCTURE OF AL-6MN-3MG ALLOY SEM IMAGE: Structure of as-extruded Al-6Mn-3Mg alloy: a) IM material; b) RS material Relatively coarse particles observed in IM microstructure The size of particles in IM material is varied within µ m. Large particles were fractured during the hot extrusion that resulted in the increase of the material porosity. Rapid solidification results in efficient refining of the particles, which are nm in size

16 EFFECT OF RAPID SOLIDIFICATION ON MICROSTRUCTURE OF AL-6MN-3MG ALLOY A preliminary microstructure of as-extruded RS material and the microstructure of the sample annealed at 500ºC / 7 day. Particles coarsening are attained by long-term annealing of RS material at 500ºC and then particles size reached 1-3 µm after annealing at 500ºC / 7 days.

17 EFFECT OF RAPID SOLIDIFICATION ON MICROSTRUCTURE OF MG-AL ALLOYS Optical micrographs of as-casta) Mg-5Al alloy b) Mg-15Al alloy c) Mg-30Al alloy ingots. Microstructure consists of two constituents (i) α-mg solid and (ii) Eutectic. The eutectic structure existing along the grain boundaries increases in amount with increasing Al content. The microstructure in the Mg-30Al alloy is almost entirely made up of the eutectic constituent.

18 EFFECT OF RAPID SOLIDIFICATION ON MICROSTRUCTURE OF MG-AL ALLOYS Optical micrographs of RSP flakes (a) (c) transverse and (d) (f) longitudinal sections. (a) and (d) Mg-5Al, (b) and (e) Mg-15Al, (c) and (f) Mg-30Al alloys. Well-developed dendritic structures are observed in the transverse direction Dendrite arm spacing is very good which is about 2 µm in the RSP Mg-15Al flakes which occurred during RSP.

19 EFFECT OF RAPID SOLIDIFICATION ON MECHANICAL PROPERTIES OF MG-AL ALLOYS As Al content increases, the hardness of the alloys also increased. It increased from about 50 VHN for the Mg-5Al ingot to about 185 VHN for the Mg-30Al ingot. Flake material has a higher hardness than as-cast ingot material due to the fine microstructure. The hardness of the flakes also increased from about 60 VHN for Mg-5Al to about 210 VHN for Mg-30Al.

20 EFFECT OF RAPID SOLIDIFICATION ON MECHANICAL PROPERTIES OF MG-AL ALLOYS The tensile strength increases with increasing Al content. As a Al content increases, the elongation decreases.

21 EFFECT OF RAPID SOLIDIFICATION ON MICROSTRUCTURE OF TI-6A1-4V-1B-0.5Y ALLOY SEM image (backscattered) shows Needle-shaped boride phase (black), Cuboidal yttria particles (white) and Martensitic titanium matrix (grey) in Ti-6A1-4V-1B-0.5Y ingot solidified in a water-cooled copper hearth.

22 EFFECT OF RAPID SOLIDIFICATION ON MICROSTRUCTURE OF TI-6A1-4V-1B-0.5Y ALLOY SEM image shows the cross-section of a multi-layer meltspun fibre. For a single layer, there are two microstructural zones: A. the equiaxed dendrite zone at free side (F) and B. the columnar grain zone at wheel side (W). The coarse yttria particles (white) can also be seen in this micrograph.

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24 EFFECT OF RAPID SOLIDIFICATION ON MICROSTRUCTURE OF TI-6A1-4V-1B-0.5Y ALLOY Bright-field TEM image of the consolidated RS Ti-6A1-V-1B-0.5Y alloy shows- the detailed morphology of boride and yttria particles in the titanium matrix.

25 EFFECTS OF COOLING RATE ON TENSILE PROPERTIES OF A TI-MO-AI ALLOY Production method UTS (MPa) RA(%) Casting Cast + Hot worked /10000 cooling + Hot isostatic pressing Flake / cooling +Hot isostatic pressing During rapid solidification of as-cast Ti-Mo-Al alloy, both strength and ductility increase with cooling rate.

26 CONCLUSIONS New production techniques and use of new materials are very important considerations in the high technology industries. RS has several barriers- need for optimization of processing routes needs heavy capital investment and competitive new technologies present high cost of RS materials Elevated temperature aluminum alloys have more potential than high-strength aluminum alloy. Intermetallic compounds based on aluminum are the major potential area for hightemperature applications. Low density magnesium systems based on magnesium are the major potential area for requiring optimization. The hardness and tensile strength of the RSP alloys is higher than in the IM alloys due to the fine size of the α-mg and β-mg-al phases. Refined and more desirable microstructures can be attained by rapid solidification of titanium from conventional alloys.

27 THANK YOU