Crystal Structure of Aluminum, Zinc, and their

AlloysBy: Omar Fajardo

Sebastian Henao

Devin Baines

ENGR45, F2014, SRJC

Purpose

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

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 26.9815385(7)

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

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

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)]

38 (263) 32-37 (221-255) 40-46 (276-317) 45-50 (310-345) 58-64 (400-441) 45-47 (310-324)

Yield strength - 0.2% offset [ksi (MPa)]

29 (200) 30 (206) 31 (214) 39 (269) 54 (372) 37 (255)

Elongation [% in 2"] 1-2 1-2 1-3 1-3 3-6 8-11

Shear strength [ksi (MPa)] - 35 (241) 37 (255) - 42 (290) 33 (228)

Hardness [Brinell] 85 85-90 89-105 89-105 110-120 90-110

Impact strength [ft·lbf (J)] 156 (20) - 193 (25) - 353 (47) 433 (58)

Fatigue strength rotary bend in 5x108 cycles [ksi (MPa)]

- 7.5 (52) 15 (103) - 25 (172) 15 (103)

Compressive yield strength 0.1% offset [ksi (MPa)]

29 (199) 31 (214) 33 (227) 34 (234) 48 (331) 37 (255)

Modulus of elasticity [psi x 106 (MPa x 103)]

12.4 (85.5) 12.47 (85.5) 12.07 (82.7) 12.07 (82.7) 11.37 (77.9) 11.37 (77.9)

Poisson's ratio 0.29 0.29 0.30 0.30 0.32 0.32

Physical properties Sand cast Permanent mold Sand cast Permanent mold Sand cast Permanent mold

Density [lbm/in3 (g/cm3)] .227 (6.3) 0.227 (6.3) 0.218 (6.0) 0.218 (6.0) 0.181 (5.0) 0.181 (5.0)

Melting Range [°F (°C)] 707-759 (375-404) 707-759 (375-404) 710-810 (377-432) 710-810 (377-432) 708-903 (376-484) 708-903 (376-484)

Electrical Conductivity [S/m (%IACS)]

1.61 (27.7) 1.61 (27.7) 1.64 (28.3) 1.64 (28.3) 1.72 (29.7) 1.72 (29.7)

Thermal Conductivity [BTU/hr/ft2/°R (W/m/°K)]

66.3 (114.7) 66.3 (114.7) 67.1 (116.1) 67.1 (116.1) 72.5 (125.5) 72.5 (125.5)

CTE [68-212°F µin/in/°R (100-200°C µm/mm/°K)]

12.9 (23.3) 12.9 (23.3) 13.4 (24.2) 13.4 (24.2) 14.4 (26.0) 14.4 (26.0)

Specific Heat [BTU/lbm/°R (J/kg/°K)]

.104 (435) .104 (435) .107 (448) .107 (448) .125 (523) .125 (523)

Pattern of Die Shrinkage [in/ft (mm/m)]

1/8 (10.4) 1/8 (10.4) 5/32 (13.0) 5/32 (13.0) 5/32 (13.0) 5/32 (13.0)

Chemical Specification (per ASTM) (% by Weight)

ZA8ZA12 ZA27

Composition Ingot Casting Ingot Casting Ingot Casting

Al 8.2-8.8 8.0-8.8 10.8-11.5 10.5-11.5 25.5-28.0 25.0-28.0

Mg .020-.030 .015-.030 .020-.030 .015-.030 .012-.020 .010-.020

Cu 0.8-1.3 0.8-1.3 0.5-1.2 0.5-1.2 2.0-2.5 2.0-2.5

Fe (max) .065 .075 .065 .075 .072 .075

Pb (max) .005 .006 .005 .006 .005 .006

Cd .005 .006 .005 .006 .005 .006

Sn (max) .002 .003 .002 .003 .002 .003

Ni (other)x10 - - - - - -

Zn Bal Bal Bal Bal Bal Bal

Color Code ASTM B908

Blue Blue Orange Orange Purple Purple

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.

Aluminum

Zinc

Pure Zinc

Procedure

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.

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

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.

Eutectic Diagram

α = Al rich FCC phase

ß = Zn rich FCC phase

η = Zn rich HCP phase

L = Liquid Solution

Al-Zn Phase Diagram

20% Zn, 80% Al

50% Zn, 50% Al

80% Zn, 20% Al

100% Zn

Sources

Aluminum - http://en.wikipedia.org/wiki/Aluminium

Zinc- http://en.wikipedia.org/wiki/Zinc

Zinc/Aluminum - http://en.wikipedia.org/wiki/Zinc_aluminium