AM-lite – A Diecasting Magnesium Alloy with High Quality Surface Finish

AM-lite is a new magnesium high pressure die casting alloy aimed at a wide range of applications that currently utilise magnesium alloy AZ91D, aluminium and zinc die casting alloys, and also injection moulded plastics. While retaining advantages common to magnesium alloys such as light weight, AM-lite offers superior as-cast surface quality and improved surface definition, and can fill thinner sections than either AZ91D or other magnesium alloys. AM-lite is particularly suitable for die castings requiring electroplating or other decorative surface finishing processes such as powder coating and painting.

Figure 1. Electroplated AM-lite diecasting.

Main Attributes of AM-lite

The main attributes of AM-lite are:

  • Reduced costs
  • Low density
  • Similar electroplating process to zinc alloys
  • Reduced rejects in other coating processes
  • Excellent diecastability
  • High quality as-cast surface finish
  • Improved mechanical properties
  • Wide operating window for die casting parameters
  • Melt is resistant to burning and excessive oxidation

Key Advantages of AM-lite

Advantages of AM-lite Compared to Zinc Diecasting

Compared to zinc die casting alloys AM-lite offers:

  • Significantly reduced costs (metal costs reduced by 70-75%)
  • Light weight (70% reduction of density)
  • Similar electroplating process
  • Higher design strength
  • Reduced defects in surface coating operations

Advantages of AM-lite Compared to Magnesium Alloy AZ91D

Compared to magnesium AZ91D die casting alloy AM-lite offers:

  • Reduced costs (lower diecasting and surface finishing costs)
  • Improved die castability
  • Better as-cast surface finish
  • Electroplating process similar to zinc diecastings
  • Reduced defects in surface finishing
  • Higher strength
  • Improved recyclability

Advantages of AM-lite Compared to Aluminium Diecasting

Compared to aluminium die casting alloys AM-lite offers:

  • Reduced costs (lower surface finishing costs)
  • Lighter weight (26% reduction in density)
  • Superior as-cast surface finish
  • Improved electroplating

Advantages of AM-lite Compared to Plastics

Compared to plastics AM-lite offers:

  • Reduced costs (stiffness provides design freedom)
  • Metallic “feel”
  • Higher strength and stiffness
  • Increased design greedom
  • Electrical conductivity for electromagnetic shielding
  • Good thermal conductivity

Diecasting of AM-lite

AM-lite is suitable for both hot chamber and cold chamber diecasting processes.

The high die castability of AM-lite allows for:

  • Production of very thin sections
  • Reproduction of fine detail from the die
  • Reduction of runner cross sectional area by 25% (higher yield)
  • Wider operating window
  • Greater stability of operation
  • Improved productivity

Extensive industrial trials have demonstrated: reduced cover gas usage; low melt losses (~4% for AZ91, ~1% for AM-lite); reduced burning during removal of dross and sludge; and significantly reduced fuming.

Surface Finishing

The high quality surface finish of AM-lite die castings makes AM-lite highly suitable for surface finishing operations such as electroplating, painting and electrophoretic coating. In addition, the smooth as-cast surface of AM-lite die castings reduces the need for costly polishing and buffing operations. Elimination of secondary buffing, commonly required for electroplating of conventional magnesium alloys, can yield major cost savings. The high creep strength of AM-lite substantially reduces blister defects that can arise during baking of painted and powder coated surfaces.

Mirror finish on as-cast AM-lite surface

Figure 2. Mirror finish on as-cast AM-lite surface

Electroplating

An electroplating process has been developed specifically for AM-lite by MacDermid Inc. Compared to electroplating of AZ91D diecastings, MacDermid’s Bondal Mg process for AM-lite is much simpler and cheaper. The resultant electroplated coating is vastly superior to coatings on AZ91Dand aluminium alloys (which are extremely difficult and expensive) and is of similar quality to coatings on zinc diecastings.

Typical Properties of AM-lite

Table 1. Mechanical properties of AM-lite at room temperature (2 mm thick die castings).

Property

Value

Hardness

VHN (300g)

85-90

Brinell

76-80

0.2% Proof Stress

160-170

Ultimate Tensile Strength (MPa)

230-250

Fracture Elongation % (50mm)

3-4

Young’s Modulus (GPa)

45.3

Poisson’s Ratio

0.35

Shear Modulus (GPa)

16.8

Compressive 0.2% Proof Stress (MPa)

150

Compressive Strength (MPa)

446

Table 2. Physical properties of AM-Lite.

Property

Value

Density @ 20°C

2.0

Solidifcation Range (°C)

585-330

Latent Heat (kJ/kg)

340

Specific Heat @ 25°C (kJ/kg.°C)

0.95

Heat Release During Casting (600-259°C) (kJ/cm3)

1.0

Co-Efficient of Thermal Expansion (K-1)

24.9x10-6

Handling AM-lite

As for all magnesium alloys, precautions should be taken when handling and melting AM-lite. These precautions are broadly outlined in Advanced Magnesium Technologies’ Technical Information Sheet “Safe Handling of Magnesium”.

When handling AM-lite in the molten state it is recommended that the AM-cover protective gas system is used. Advanced Magnesium Technologies’ Technical Information Sheet “The AM-cover System for Protecting Molten Magnesium” provides an introduction to the advantages and usage of AM-cover.

For in-cell recycling of diecasting returns it is recommended that the AM-converter technology is used. Advanced Magnesium Technologies’ Technical Information Sheet. “AM-converter – the solution for efficient magnesium melting” provides an introduction to this technology.

Source: Advanced Magnesium Technologies

For more information on this source please visit Advanced Magnesium Technologies

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