Grain refinement of aluminium alloys using grain refiners

“GRAIN REFINEMENT OF ALUMINIUM ALLOYS BY ADDING grain refiners”

Department of mechanical engineering

Submitted by Ricky Vincent (1ep10me083)Md.Rehan Alam (1ep10me053)Bishwash Singh (1ep10me017)Md. Imran Ansari (1ep10me051)

Under the guidance of

Prof Sahadeva G.N

In Figure ,each of the light areas is called a grain, or crystal, which is the region of space occupied by a continuous crystal lattice.  The dark lines surrounding the grains are grain boundaries.

Grain is the region of space occupied by a continuous crystal lattice.

Grain refinement means modifying the size of equiaxed grains in a casting.

Generally grain refinement refers to decreasing the average grain size.It is used to modify the structure of the Aluminium alloy to improve cast product specific properties.

INTRODUCTION

INTRODUCTION Aluminium  is a chemical element in the boron group with symbol Al

 and  atomic number 13.. It is a silvery white, soft, ductile metal. Aluminium is the third most abundant element (after oxygen and silicon)It is remarkable for the metal's low density and for its ability to resist corrosion

and soft, durable, lightweight, ductile and malleable metal.

PERCENTAGE OF ALUMINIUM ALLOYS USED IN INDUSTRIES

COMPOSITION OF AA 356 & IT’S PROPERTIES

AA 356 contains approximately 0.3%Mg, 7%Si and approximately 92.7 % Al.It also contains minute quantities of Fe, Mn, Cu,Zn and Ti.Hard, odorless solid whose color ranges from silver to gray.Melting Temperature is 660 deg©. Density is 2.7 gm/cm^3.Modulus of Elasticity is 70-80 Gpa.The ultimate tensile strength is 40 Ksi .Machinability =3 (average)

INTRODUCTION – AA356AA 356 aluminum, also called aluminum alloy A356 and aluminum casting alloy.It is the standard alloy for casting aluminum. The alloy is widely used in the avionics, engineering and automotive industries to make aircraft fittings, transmission cases, wheels, tool parts, bridge parts, pump parts and control parts. AA 356 aluminum is tough, corrosion-resistant and performs well in high-pressure and high-temperature conditions, making it ideal for various high-wear applications.The BHN of AA 356 aluminum is 80, which means the substance can withstand high loads without buckling.

ADVANTAGESAluminum is light - about 1/3 the density of steel Corrosion resistant (No painting for protection) Aluminum is very good at conducting heat (Heating and Cooling applications) It is easy to cast, or die-cast to precise and complex shapes.Recyclability (using 5% of energy from smelting and most of the used Al is from scrap –process or recycle products) No significant health hazards to health or to envmt.

DISADVANTAGESaluminum is not particularly strong - the strongest varieties are around 75,000 psi tensile strength

aluminum is not very hard - it's easy to scratch 

aluminum is more expensive than steel of the same strength

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APPLICATIONSTransportation (automobiles, aircraft, trucks, railway cars, marine vessels, bicycles, etc.) as sheet, tube, castings, etc.Packaging (cans, foil, frame of etc.)Construction (windows, doors, siding, building wire, etc.).A wide range of household items, from cooking utensils to baseball bats, watches.Street lighting poles, sailing ship masts, walking poles, etc.Outer shells of consumer electronics, also cases for equipment e.g. photographic equipment, MacBook Pro's casingElectrical transmission lines for power distributionPowdered aluminium is used in paint, and in pyrotechnics such as solid rocket fuels and thermite.

GRAIN GROWTH & NUCLEATION

Molten metal continues to solidify around nuclei.The nuclei and the metal solidifying around them continuously release latent heat .As the temperature decreases due to cooling the nuclei grow rapidly and atoms attach themselves in dendritic formation.When more and more atoms attach themselves in a particular direction, they form a trunk like that of a tree.Nucleation is the process of forming a nucleus. It is the initial process in crystallization.It is the process in which ions, atoms, or molecules arrange themselves in a pattern characteristic of a crystalline solid, forming a site in which additional particles deposit as the crystal grows.

HOMOGENEOUS & HETEROGENEOUS NUCLEATION

When nucleation takes place in a liquid metal without the help of any impurities ,then it is known as homogeneous nucleation. Eg.perfectly homogeneous materials such as pure liquid metals.When nucleation takes place in liquid metal with the help of impurities , then it is known as heterogeneous nucleation. Eg. Diet Coke and Mentos eruption. Nucleation normally occurs at nucleation sites on surfaces contacting the liquid or vapor. Suspended particles or minute bubbles also provide nucleation sites.

EXPERIMENTAL SET-UP

Specimen size 22 to 26 mm Duration 90 minsPreparation of dieMelting of Al-356DegassingAdding inoculantsSolidification and preparation of specimenComparing mechanical properties for the various cases (%)

VICKERS HARDNESS TEST & TENSILE TEST

VICKERS HARDNESS TEST RESULTS

TENSILE TEST

MICROSTRUCTURE1) Microstructure ofAA-356 with 0.4wt% of (Al-5Ti-1B) grain refiner2) Microstructure ofAA-356 with 0.6wt% of (Al-5Ti-1B)(500X)3) Microstructure ofAA-356 with 0.8wt% of (Al-5Ti-1B) The porosities are reduced to maximum extent and grain

refinement has been improved which leads to improve in fluidity for complex mold designs.

MICROSTRUCTURE

Microstructure ofAA-356 with 0.6wt% of (Al-5Ti-1B))Microstructure ofAA-356 with 0.8wt% of (Al-5Ti-1B) (100X)The grain refinement is better at 0.6 solid fraction compare to 0.8% grain refinement solid fraction. The cavitations occurs in the melt in large extent which gives rise to the formations tiny cavities & discontinues. These cavities expand and compress instantaneously collapses due to tensile and compression forces produced in the formation of nuclei of the solid phases, by these immediately the heterogeneous nucleation starts at large number and produces very small in grain sizes with globular uniform grain structure.

CONCLUSIONGrain refinement means modifying the size of equiaxed grains in a casting(decreasing the average grain size). Grain refinement is used to modify the structure of Al-alloy to improve the microstructure and cast product specific properties such as tensile strength, hardness etc……Al-356 is widely used in industries and this alloy gives maximum properties for material characteristics and to improve properties we are examining Al-356 by the addition of 0.05% of inoculant Al-5Ti-1B.Microstructure changes--the porosities are reduced to maximum extent and grain refinement has been improved which leads to improve in fluidity for complex mold designs.

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