New low-cost, lightweight magnesium sheet alloy with good formability for automotive applications; 1.5x stronger than aluminum
24 July 2017
A research team at Japan’s National Institute for Materials Science (NIMS) and Nagaoka University of Technology has developed a new high-strength magnesium sheet alloy (Mg–1.1Al–0.3Ca–0.2Mn–0.3Zn) that has excellent room-temperature formability comparable to that of the aluminum sheet metal currently used in body panels of some automobiles.
The magnesium alloy becomes stronger than aluminum alloy after a heat treatment, uses only common metals, and could be a low-cost, lightweight sheet metal for automotive applications. A paper on the work is published in the journal Scripta Materialia.
Lightweight magnesium (Mg) alloys have attracted considerable attention for potential applications in the automotive industries. However, the low strength or poor formability at room temperature (RT) hinders the wider applications of wrought Mg alloy sheets. In general, stretch formability and yield strength are inversely correlated; therefore, it is difficult to obtain both high strength and high formability.
… Recent studies have reported that dilute Mg–Al–Ca–Mn (AXM) system could be industrially viable wrought alloys due to their extraordinary high-speed extrudability and rapid age-hardening response. If this system can be used as sheet alloys as well, then a huge impact on the automotive industries is expected. Therefore, attempts were made by the present authors to develop sheet alloys from the AXM system. During the processing of Mg–1.1Al–0.3Ca–0.2Mn at.% [atomic percentage] alloy, it was found that the addition of a small amount of Zn (0.3 at.%) to the Mg–1.1Al–0.3Ca–0.2Mn alloy substantially improved the stretch formability. Additionally, subsequent short time aging led to a significant increase in the strength of the resultant Zn-containing alloy. The purpose of the present paper is thus to report results of (i) assessments of mechanical properties of the T4 and T6 treated Mg–1.1Al–0.3Ca–0.2Mn alloy sheets, with or without Zn additions, and (ii) characterization of the microstructures and textures of these sheets.
—Bian et al.
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| Comparison of newly developed and conventional magnesium alloy sheets after they were subjected to Erichsen tests. Credit: National Institute for Materials Science. Click to enlarge. |
Named AXMZ1000, the newly developed alloy has room temperature formability comparable to that of medium strength aluminum alloys that are used in some automobile bodies. In addition, the new alloy is 1.5 to 2.0 times stronger than the aluminum alloy.
The addition of very small amounts of zinc (Zn) and manganese (Mn) led to the formation of fine grain structures; the high strength was accomplished by adding aluminum (Al) and calcium (Ca), which induced the strengthening of the alloy by the formation of atomic clusters.
The newly developed alloy is composed of only common metals, so the material cost is not expensive. It can be rolled into sheets using simple processes and heat treatments commonly used for aluminum alloys.
This study was conducted as a part of the JST Advanced Low Carbon Technology Research and Development Program (ALCA).
Resources
M. Z. Bian, T. T. Sasaki, B. C. Suh, T. Nakata, S. Kamado, K. Hono (2017) “A heat-treatable Mg–Al–Ca–Mn–Zn sheet alloy with good room temperature formability” Scripta Materialia Vol. 138, page 151 doi: 10.1016/j.scriptamat.2017.05.034
A: How much would it cost ?
B: What about fire resistance.
Posted by: mahonj | 24 July 2017 at 08:08 AM
For over 100 years, ICEVs manufacturers kept making their vehicles larger and heavier, justifying-requiring, larger stronger ICEs, consuming more fossil fuel and polluting more and more. They went all the way to 9,000 lbs, 9 mpg Hummer-1
No real efforts were made to make lighter more efficient units. Even today, many still think that they need a 5000+ lbs ICEV or BEV to go to work or to show neighbors how rich they are.
Of course much stronger-lighter vehicles could be designed and built at little extra cost, if any. Lighter e-units (BEVs/FCEVs) could give more range with smaller batteries/FCs and run on less energy.
More automation and standardization could keep mass production cost low.
Posted by: HarveyD | 24 July 2017 at 12:31 PM
Not sure what the point is of the above post, aside from general ranting.
Magnesium has been in use for decades but typically in parts manufactured by casting or forging. Notably, the old air-cooled VW Beetle used cast magnesium crankcases. Fire resistance can be a problem area. The good thing is that magnesium conducts heat quickly, so if the part has a decent thickness to it (e.g. crankcases produced by casting) it is pretty resistant to catching fire from a local hot spot (e.g. match or lighter or burning piece of paper or some such). If the whole part is surrounded by fire so that there is nowhere to conduct the heat TO, then yes, it's going to catch fire - and when it does, look out. Water will not extinguish burning magnesium.
In the case of sheet metal, the (presumably) thin cross section will allow it to heat up quickly and catch fire more easily ...
Magnesium is not good for corrosion resistance, either. It can be painted to prevent corrosion but anything that disrupts the painted surface will lead to corrosion.
Probably this new manufacturing process will have some applications but don't expect entire bodyshells to be built from magnesium any time soon.
https://www.youtube.com/watch?v=cSusDFuaAms
Posted by: Brian P | 24 July 2017 at 04:51 PM
This alloy could always be clad with a layer of aluminum to get better corrosion resistance. IIRC "Alclad" is commonly used in light aircraft. Aluminum is also extrudable so it may be feasible to build machines to co-extrude forms which are pre-clad.
Posted by: Engineer-Poet | 24 July 2017 at 06:26 PM
Automotive currently utilizes magnesium. They have learned better organic coatings and better assembly practices to prevent corrosion. It's not as simple as preventing steel corrosion even though high quality magnesium in salt spray tests do better than steel by factor of seven and better than aluminum by a factor of three. The problem is galvanic corrosion with steel. The assembly has to have water drainage and air gaps when close to steel. Aluminum is o.k. and a good material to utilize as washers on bolts if connecting steel and magnesium.
Posted by: Trees | 25 July 2017 at 06:13 AM
Oh, my friend in HS had a magnesium boat. A small row boat type that flew with small outboard. No corrosion, but no steel either. Since aluminum is utilized in boating, magnesium works well and better than stainless steel. I worked for a company that made stainless steel boat brackets for marine industry. They found out their brackets caused galvanic corrosion on outboards and quietly left the business.
Posted by: Trees | 25 July 2017 at 06:17 AM
Most cars used to rust in the first 4-5 years when used on salted roads. Now, most cars can be used without developing rust for 15 to 20 years in the same conditions.
Aluminum, new magnesium alloys and recent composites could do about the same while reducing body weight by 30% to 40%. It would help to turn current short range BEVs into longer range units using less e-energy and/or H2?
Posted by: HarveyD | 25 July 2017 at 07:15 AM