Hitachi Metals : Developing a High-Ductility and High-Strength Magnesium Alloy

December 1, 2022
Hitachi Metals, Ltd.

Hitachi Metals, Ltd. ("Hitachi Metals") announced that it has developed a new magnesium alloy, which is rare-earth-free and has high ductility and strength, in cooperation with the National Institute for Materials Science (NIMS). Since the alloy does not contain elements that are considered to have properties that are damaging to the living body or compositions that are difficult to decompose in the environment of the body, it also has superior biocompatibility. Hitachi Metals will deploy the technology it has developed as one solution for growing markets such as mobility, welfare equipment and medical equipment.

1. Background

In the mobility field, where it is necessary to reduce CO₂ emissions during transportation, and in the welfare equipment field which includes wheelchairs that must be easy to handle, it is necessary to reduce the weight of parts that must be strong and have excellent workability, and there is demand for materials that satisfy these high-level conditions.
In addition, the medical device field including stents, which are implanted in people's bodies, and materials used to secure fractured bones in place, which have excellent mechanical properties (strength and ductility), high biocompatibility, or bio-absorbability, which indicates the ability for your body to absorb the materials as the damaged area heals, are drawing interest.
In this environment, a magnesium alloy that is the lightest and the most bioabsorbable of the commercialized metal materials, is drawing attention. However, to increase the applicability of the alloy to more products, it was necessary to improve the strength and workability of the alloy.

2. Outline

• Photo: Examples of processing from cast ingots
  (Left: extrusion molding (diameter: 64mm),
  Right: wire drawing (diameter: 1.3mm))

Hitachi Metals and NIMS have jointly developed a high-ductility and high-strength magnesium alloy which has high ductility (elongation: >20%), strength (proof stress: > 300MPa) and biocompatibility because it does not contain elements whose properties are damaging to the living body or substances that are difficult for the body to decompose.
This high-ductility and high-strength magnesium alloy achieves high ductility and high strength by promoting both grain boundary sliding^*1 and grain boundary strengthening^*2 through the grain boundary segregation^*3 of added trace elements (see "Figure"). In addition, it enables ductility and strength to be controlled by selecting the added trace elements (see "Graph"). In addition, it has higher strength and ductility than the WE43 alloy (Mg-rare earth-yttrium series alloy, proof stress: 160MPa, elongation: 6%), which has an established records of application in stents in overseas countries, and it does not contain elements that have been identified as having properties that are damaging to the living body or compositions that are difficult to decompose in the environment of the body. Furthermore, thanks to its high strength that preserves high ductility, it is easy to mold into a size and shape that fulfills the customer's needs through extrusion molding, pultrusion molding, rolling, etc. (see the photos).
It can be expected that this alloy that achieves both high ductility and high strength will be used as a material to support the long, healthy lives of the people in a low-carbon society, and we will deploy it in solutions for related markets. Hitachi Metals will also exhibit this product for the first time at the 2nd Sustainable Materials Exhibition to be held at Makuhari Messe from December 7.

- Figure: Mechanism for developing this high strength, high ductility alloy

Both high strength and high ductility are achieved by segregating the element X at the grain boundary, which leads to a stronger grain boundary, and existing the trace element Y in the crystal grain and at the grain boundary, which promotes the sliding of the grain boundary.

- Graph: Tensile properties of the extrusion-molded developed alloy and the general-purpose alloy

Comparison of the properties of alloy A and a general-purpose material (when the properties of the general-purpose material are considered to be 1)

Application	General-purpose material	Strength	Ductility	Weight reduction
Stent material	WE43	2 times	3 times or more	1.5 times
Case material	AZ31C	2 times or more	4 times	1.4 times or more
High-end cast wheel material/ wheelchair frame material	AZ80A ZK60A	1.5 times or more	5 times	1.1 to 1.2 times

*Developed products A to C have different alloy compositions.
Alloy A focuses on strength while alloy C focuses on ductility. Alloy B is positioned in between them. Hitachi Metals will provide alloys that meet the customer's needs.*1 Grain boundary sliding : Deformation caused by relative sliding (displacement) of two crystals to either side of a crystal grain boundary.
When this advances, the ductility of the material is improved. *2 Grain boundary strengthening : This method strengthens a material by segregating a part of the solute atoms into a crystal grain boundary.*3 Grain boundary segregation : A phenomenon where some of the solute atoms collect at the crystal grain boundary, which promotes the sliding of the grain boundary and the strengthening of the grain boundary.

Contact for customers:
Global Research & Innovative Technology center, Hitachi Metals, Ltd.
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Contact for press:
Corporate Communications Dept., Hitachi Metals, Ltd.
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