Title: Chapter 6 Overview
1Chapter 6 Overview
- Four major alloy groups most common
- Aluminum, magnesium, zinc and ZA
- These alloys have a range of properties and
characteristics - Properties are slightly less but overlapping with
sheet steels - Properties are greater than but somewhat
overlapping with high strength plastic resins
2Chapter 6 Objectives
- Correctly identify the most common alloy from
each major group - Identify the alloy with the highest strength
- Identify the major alloying ingredients from an
alloy specification - List nine important criteria used to select an
alloy for a particular job
3New Terms
- Tensile strength
- Maximum stress achieved when pulling a test
specimen to failure in the direction of its
length - Yield strength
- Level of strength at which elastic strain becomes
plastic strain
4New Terms
- Elongation
- Amount of permanent extension in the vicinity of
the fracture in the tension test - Modulus of elasticity
- Slope of the elastic portion of the stress-strain
curve in mechanical testing
5Mechanical Properties
- Properties include tensile strength (ultimate),
yield strength, elongation (ductility), and
modulus of elasticity (MOE) - Predicts how alloy will react to stressed
condition - Strong alloy high values of tensile and yield
strengths and MOE, and low values of elongation - Weak alloy low strengths and MOE, and higher
values of elongation
6Aluminum Alloy Characteristics
- Has a specific gravity of 2.7 lightweight
- As a base, it has 3 primary alloying ingredients
silicon, copper and magnesium - All the other ingredients can be called
impurities - In some cases impurities must be controlled at
specific levels, in other cases the level of
impurity may be an economic compromise
7Aluminum Product Applications
- 380 aluminum alloy most commonly used
- Lawn mower housings, electronics chassis, engine
components, home appliances, tools - 383 and 384 for intricate components, improved
die filling, improved resistance to hot cracking - 360 improved corrosion resistance, superior
strength
8Aluminum Product Applications
- 443 greatest ductility
- 413 excellent pressure tightness, highly fluid
and useful for intricate detail - 390 greatest wear resistance
- 518 very good corrosion resistance and
ductility used in marine and aircraft hardware
and also in escalators
9Magnesium Alloy Characteristics
- Has a specific gravity of 1.74 lightest
commonly used structural metal - As a base, it has 4 primary alloying ingredients
- Aluminum, zinc, manganese and silicon
- All other ingredients are impurities and are
controlled to maximum limits
10Magnesium Product Applications
- AZ91D found in drive train automotive components
as well as handheld and laptop computers - AM60A has good elongation and toughness used in
automotive wheels and steering wheels and archery
equipment - AS41A has creep strength at elevated temperatures
11Zinc Alloy Characteristics
- Has a specific gravity of 7.0 one of the
heavier commonly used structural metal - As a base, has 3 primary alloying ingredients
- Aluminum, magnesium and copper
- All other ingredients are impurities and are
controlled to maximum limits - Sometimes referred to as Zamak
- Highest purity of the die casting alloys
12Zinc Alloy Product Applications
- 3 zinc specified most frequently for functional
and hardware castings - 5 zinc has higher tensile strength, hardness,
creep resistance automotive locks - 7 zinc has slightly lower hardness and higher
ductility higher fluidity than either 3 or 5
could be a better choice for thinner walls and
finer detail
13ZA Alloy Characteristics
- Developed in 1950s
- Alloys of zinc, aluminum and copper
- Superior properties over Zinc Alloys
- Wear resistance
- Creep resistance
- Higher strength
- Lighter weight
149 Criteria Alloy Cost
- An important factor in overall product cost
- Cost of alloy should be converted to a volume
basis - Aluminum alloys usually have lowest cost per
cubic inch - Magnesium and zinc can be competitive because can
be cast with thinner walls and at reduced volume
159 Criteria Process Cost
- An important component of overall product cost
- Alloys run with hot chamber process usually run
in smaller DCMs and at higher production rates
than equivalent casting with the cold chamber
process - Maintenance and replacement costs can vary
significantly
169 Criteria Structural Properties
- Aluminum alloys have the highest modulus of
elasticity (MOE) - Relatively high strength/low density
- Magnesium has lower strength and rigidity
- Competitive with aluminum in some applications
through strategic placement of reinforcing ribs - ZA alloys offer highest tensile and yield
strengths
179 Criteria Minimum Weight
- Magnesium alloys are the dominant choice if
weight must be minimized
189 Criteria Impact Strength and Dent Resistance
- Highest among the zinc (Zamak) alloys
- Diminishes sharply as temperature is reduced
below 32ºF (0ºC) - Impact resistance of aluminum and magnesium
alloys varies within each alloy group
199 Criteria Surface Finish
- Surface finish best achieved by the zinc and
magnesium alloys - Die steel surface quality is essential to casting
surface quality
209 Criteria Corrosion Resistance
- Corrosion resistance varies from alloy to alloy
and within an alloy group - Can be improved with low-cost surface treatments
219 Criteria Bearing Properties and Wear
Resistance
- Bearing properties and wear resistance
- Good for hydrodynamic bearing applications
- If partial lubrication only, ZA alloys and 390
aluminum resistant to abrasion and wear
229 Criteria Machineability
- Machineability of all alloys excellent
- Magnesium alloys offer best machinability in
terms of tool life, energy consumption and low
cutting forces
23Freezing
- Same as water
- Various metals freeze at a particular temperature
for that metal - Time versus temperature chart is slightly
different than that for elements (pure metals)
and compounds
24Quality
- Alloy chemical composition is controlled by an
ASTM, American Society for Testing and Materials,
specification - Each die casting plan has a method for
maintaining alloy quality - Begins with purchasing of material, and continues
through manufacturing process and shipment
25Quality Cleanliness
- Cleanliness component of alloy quality
- Not as easily checked as chemical composition
- Each time alloy is melted, some material is
oxidized - Oxides are impurities in alloy that could affect
the castings properties if not removed - Processes to minimize amount of oxidation and
remove the oxides from the alloy
26Summary
- Designers consider range of issues when creating
a die casting - Each alloy has different mechanical properties
tensile strength, yield strength, elongation, and
MOE - The alloy chosen must be appropriate to the die
castings application - Alloy selection is based on characteristics and
properties of the alloys in 9 categories