Chapter 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
6-1
Chapter 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
6-2
New 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
6-3
New 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
6-4
Mechanical 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
6-5
Aluminum 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
6-6
Aluminum 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
6-7
Aluminum 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
6-8
Magnesium 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
6-9
Magnesium 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
6-10
Zinc 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
6-11
Zinc 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
6-12
ZA Alloy Characteristics
 Developed in 1950’s
 Alloys of zinc, aluminum and copper
 Superior properties over
•
•
•
•
Zinc Alloys
Wear resistance
Creep resistance
Higher strength
Lighter weight
6-13
9 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
6-14
9 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
6-15
9 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
6-16
9 Criteria: Minimum Weight
 Magnesium alloys are
the dominant choice if
weight must be minimized
6-17
9 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
6-18
9 Criteria: Surface Finish
 Surface
finish best achieved by the zinc and
magnesium alloys
• Die steel surface quality is essential to casting
surface quality
6-19
9 Criteria: Corrosion Resistance
 Corrosion resistance varies
from alloy to
alloy and within an alloy group
• Can be improved with low-cost surface
treatments
6-20
9 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
6-21
9 Criteria: Machineability
 Machineability of all alloys excellent
• Magnesium alloys offer best machinability in
terms of tool life, energy consumption and low
cutting forces
6-22
Freezing
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

6-23
Quality
 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
6-24
Quality: 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 casting’s properties if not removed
• Processes to minimize amount of oxidation and
6-25
remove the oxides from the alloy
Summary
 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 casting’s application
 Alloy selection is based on characteristics
6-26
and properties of the alloys in 9 categories