Crystal Structure of Aluminum, Zinc, and their Alloys By: Omar Fajardo Sebastian Henao Devin Baines ENGR45, F2014, SRJC

Transcription

1 Crystal Structure of Aluminum, Zinc, and their Alloys By: Omar Fajardo Sebastian Henao Devin Baines ENGR45, F2014, SRJC

2 Purpose The purpose of this experiment was to examine and observe the microstructure of aluminum, zinc, and their alloys.

3 Aluminum Aluminium (or aluminum; see spelling differences) 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), and the most abundant metal in the Earth's crust. It makes up about 8% by weight of the Earth's solid surface. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals. The chief ore of aluminium is bauxite. Aluminium is remarkable for the metal's low density and for its ability to resist corrosion due to the phenomenon of passivation. Structural components made from aluminium and its alloys are vital to the aerospace industry and are important in other areas of transportation and structural materials. The most useful compounds of aluminium, at least on a weight basis, are the oxides and sulfates. Source: Wikipidia Atomic number 13 Standard atomic weight (7)

4 Zinc Zinc, in commerce also spelter, is a chemical element with symbol Zn and atomic number 30. It is the first element of group 12 of the periodic table. In some respects zinc is chemically similar to magnesium: its ion is of similar size and its only common oxidation state is +2. Zinc is the 24th most abundant element in the Earth's crust and has five stable isotopes. The most common zinc ore is sphalerite (zinc blende), a zinc sulfide mineral. The largest mineable amounts are found in Australia, Asia, and the United States. Zinc production includes froth flotation of the ore, roasting, and final extraction using electricity (electrowinning). Source: Wikipedia

5 Aluminum & Zinc Zinc-aluminium (ZA) alloys are alloys whose main constituents are zinc and aluminium. Other alloying elements include magnesium and copper. This type of alloy was originally developed for gravity casting. Noranda, New Jersey Zinc Co. Ltd., St. Joe Mineral Co. and ILZRO were the main companies that pioneered the ZA alloys between the 1950s and the 1970s. They were designed to compete with bronze, cast iron and aluminium using sand and permanent mold casting methods. Distinguishing features of ZA alloys include high as-cast strength, excellent bearing properties, as well as low energy requirements (for melting).[1] ZA alloys make good bearings because their final composition includes hard eutectic zinc-aluminium-copper particles embedded in a softer zinc-aluminium matrix. The hard particles provide a low-friction bearing surface, while the softer material wears back to provide space for lubricant to flow, similar to Babbitt metal. Source: Wikipedia

6 Properties of various zinc aluminium alloys[1] ZA8 ZA12 ZA27 Mechanical properties Sand cast Permanent mold Sand cast Permanent mold Sand cast Permanent mold Ultimate tensile strength [ksi (MPa)] Yield strength - 0.2% offset [ksi (MPa)] 38 (263) ( ) ( ) ( ) ( ) ( ) 29 (200) 30 (206) 31 (214) 39 (269) 54 (372) 37 (255) Elongation [% in 2"] Shear strength [ksi (MPa)] - 35 (241) 37 (255) - 42 (290) 33 (228) Hardness [Brinell] Impact strength [ft lbf (J)] 156 (20) (25) (47) 433 (58) Fatigue strength rotary bend in 5x10 8 cycles [ksi (MPa)] (52) 15 (103) - 25 (172) 15 (103) Compressive yield strength 0.1% offset [ksi (MPa)] Modulus of elasticity [psi x 10 6 (MPa x 10 3 )] 29 (199) 31 (214) 33 (227) 34 (234) 48 (331) 37 (255) 12.4 (85.5) (85.5) (82.7) (82.7) (77.9) (77.9) Poisson's ratio Physical properties Sand cast Permanent mold Sand cast Permanent mold Sand cast Permanent mold Density [lbm/in 3 (g/cm 3 )].227 (6.3) (6.3) (6.0) (6.0) (5.0) (5.0) Melting Range [ F ( C)] ( ) ( ) ( ) ( ) ( ) ( ) Electrical Conductivity [S/m (%IACS)] Thermal Conductivity [BTU/hr/ft 2 / R (W/m/ K)] CTE [ F µin/in/ R ( C µm/mm/ K)] Specific Heat [BTU/lbm/ R (J/kg/ K)] Pattern of Die Shrinkage [in/ft (mm/m)] 1.61 (27.7) 1.61 (27.7) 1.64 (28.3) 1.64 (28.3) 1.72 (29.7) 1.72 (29.7) 66.3 (114.7) 66.3 (114.7) 67.1 (116.1) 67.1 (116.1) 72.5 (125.5) 72.5 (125.5) 12.9 (23.3) 12.9 (23.3) 13.4 (24.2) 13.4 (24.2) 14.4 (26.0) 14.4 (26.0).104 (435).104 (435).107 (448).107 (448).125 (523).125 (523) 1/8 (10.4) 1/8 (10.4) 5/32 (13.0) 5/32 (13.0) 5/32 (13.0) 5/32 (13.0)

7 Chemical Specification (per ASTM) (% by Weight) ZA8 ZA12 ZA27 Composition Ingot Casting Ingot Casting Ingot Casting Al Mg Cu Fe (max) Pb (max) Cd Sn (max) Ni (other)x Zn Bal Bal Bal Bal Bal Bal Color Code ASTM B908 Blue Blue Orange Orange Purple Purple

8 Procedure Aluminum with 99.8% purity and zinc with 99.7% were obtained and cut into multiple small chunks. Those chunks were then weighed and grouped together to prepare them to be melted and alloyed. We decided to make five different samples. The two original samples, 100% Al and 100% Zn, one 80% Al and 20% Zn, one 50/50 Al-Zn and one 80% Zn 20% Al. Once all of the samples were weighed, we began melting the samples, followed by pouring the melted samples sandcast mold to let them cool. Each sample was cut and set in bakelite powder and was compressed into a cylindrical mold.

9 Aluminum Zinc

10 Pure Zinc

11

12 Procedure

13 Procedure Once the molds were ready, we polished each sample by sliding them in sandpaper with different grits. After polishing the samples we successfully etched each of them, with the exception of pure aluminum, by using a copper sulfate solution.

14 Etching Solution We used a deep etching technique for all of the five samples The solution we used was CuSO4 in a concentration of 200 g per liter 1.25 mol per liter

15 Failures We were not able to etch the pure aluminum sample. Over etching of 80 % zinc hypereutectoid. Under etching of 100 % Zinc Succeses We were able to observe the micro structure of most of our sample.

16 Eutectic Diagram

17 α = Al rich FCC phase ß = Zn rich FCC phase η = Zn rich HCP phase L = Liquid Solution Al-Zn Phase Diagram

18 20% Zn, 80% Al

19 50% Zn, 50% Al

20 80% Zn, 20% Al

21 100% Zn

22 Sources Aluminum - Zinc- Zinc/Aluminum -