With rise and development of magnesium alloy die-casting, number of magnesium alloy die-casting companies has increased. However, some people are wary of word "magnesium" due to safety accidents such as fires caused by improper operation during die-casting process. Based on my own work experience, I would like to discuss key safety points in magnesium alloy die-casting and machining, to promote safe production and protect personal and property safety. Different characteristics of magnesium alloys require specific protective measures and equipment.

 

Many people believe that magnesium alloy die-casting is more dangerous than aluminum alloy die-casting, being more prone to fire or explosion. However, this is unfounded. For example, many years ago, people were afraid of electricity, believing it could kill people and to stay away from it. However, now that people understand how to use electrical safety precautions, their fear has faded, and electricity has become an indispensable energy source in our lives.
Same applies to magnesium alloy die-casting. As long as necessary care is taken, magnesium alloys are no more dangerous than aluminum alloys. Large pieces of metal do not easily burn at temperatures below their initial melting point. Most of danger arises from violent reactions between molten magnesium alloy and oxygen-containing materials. These reactions generate heat and, in some cases, gases, which can lead to fires, metal splashing, and explosions. Therefore, in practice, contact between molten magnesium alloy and oxygen-containing materials must be avoided. Particular care should be taken to prevent contact between molten magnesium alloy and moist materials.
Regarding safety and precautions during magnesium alloy die-casting and machining, we will discuss the entire process from preheating magnesium alloy ingot to finished product.

Due to temperature fluctuations and relative humidity during storage and transportation, magnesium alloy ingots absorb a certain amount of moisture. Magnesium alloy ingots often exhibit signs of gas, cracking, and surface oxidation, all of which are related to moisture. Preheat magnesium alloy ingots to 150℃ before melting to remove moisture.

1. All cleaning tools and ladles must be clean, preheated, and thoroughly dried. They must be placed slowly into furnace.
2. Tools must not be surrounded by moisture-absorbing materials.
3. Molten magnesium alloy must not come into contact with wet materials. For example, floor must be clean, dry, and free of water.
4. To prevent combustion/oxidation, supply an appropriate flow of protective gas. Furnace must be well sealed to ensure an uninterrupted supply of protective gas.
5. To prevent moisture absorption, avoid using excessively long protective gas delivery pipes.
6. Minimize time furnace cover window is open during magnesium alloy ingot loading and other operations.
7. During furnace shutdown, protective gas should only be turned off when crucible temperature is below 350℃.
8. Regularly inspect crucible to prevent cracks and leaks that could cause magnesium liquid to leak.

Die casting is a preferred method for producing magnesium alloys, enabling high productivity for complex, thin-walled parts and lower die wear compared to aluminum alloys. Important precautions during die casting process:
1. Check punch frequently for leaks, as this could result in explosions and personal injury.
2. Blow out any release agent from mold to prevent splashing and injury.
3. Do not spray release agent onto material, as this could result in splashing and injury.

Although die-cast parts can almost meet precision requirements after die casting, some machining is usually required. Die-cast magnesium alloys have excellent machinability, and most die-casting companies can perform this machining. However, handling machining debris poses a fire hazard. This is because large area/volume ratio makes it easy to heat to high temperatures. Strict regulations must be adhered to when processing magnesium alloys. Magnesium alloys should never be processed on equipment used for processing other metals without established safety measures. When machining and handling magnesium alloy chips, following regulations must be observed:
1. Smoking is strictly prohibited.
2. Keep cutting tools sharp and have ample cutting angles.
3. Use a high feed rate to produce thicker chips.
4. Eliminate any fire sources that could cause chip combustion.
5. Keep machining area clean and prevent excessive chip accumulation.
6. Maintain an adequate supply of fire extinguishing agents (dry sand, cast iron chips, D-type fire extinguishers).
7. Use a special suppressive water/oil emulsion to reduce hydrogen generation and ensure an adequate supply of emulsifier.
8. Machining room must be well ventilated.
9. Place wet chips in a well-ventilated steel drum away from machining and die-casting areas.

Grinding produces magnesium dust that is highly flammable. Fire and explosion prevention measures must be carefully considered for related equipment and operations.
1. Fire, cutting, or welding are strictly prohibited in grinding area.
2. Maintain an adequate supply of fire extinguishing agents (dry sand, cast iron chips, D-type fire extinguisher).
3. Use grinding equipment suitable for magnesium alloys.
4. Use an appropriate wet dust collection system.
5. Ensure ventilation equipment is operating properly before grinding to remove accumulated hydrogen.
6. Ensure wet dust collection systems are adequately maintained and cleaned.
7. Electrical equipment on site is explosion-proof and properly grounded.
8. Do not use vacuum cleaners to collect magnesium dust unless specifically indicated for use with magnesium dust.
9. Work clothing should be flame-resistant and have no pockets.
10. Smoking is strictly prohibited.

It is important to remember that magnesium alloy ingots, die castings, and surface-treated parts will not burn unless the entire part reaches initial melting point. Due to high flame temperature (3900℃), magnesium alloys emit a dazzling white light when burning. This can be frightening to inexperienced, so it is crucial to follow safety procedures and firefighting protocols. Magnesium has a heat capacity only half that of gasoline, so magnesium alloy fires are easily extinguished with caution. However, due to presence of moisture, beware of splash explosions. Do not panic, and never use water to extinguish magnesium alloy fires, as this can cause explosions and spread fire.

 

1. A firefighting team should be available and trained.
2. Gas cylinders should not be stored in magnesium alloy melting area. If necessary, gas should be stored on a fireproof floor.
3. Necessary breathing apparatus should be available.
4. Fireproof materials should be used. Flooring in melting area should be heat-resistant and non-absorbent. Since standard cement releases moisture when metal spills, refractory bricks and specialty cement are recommended.
5. Alloy ingots, slag, processing debris, and ground magnesium powder should be stored in accordance with following guidelines:
a. Alloys should be stored separately from flammable materials.
b. Due to risk of heat and spontaneous combustion, wet machining chips should not be dried. Instead, they should be placed in a well-ventilated container and allowed to air dry.
c. Transportation vehicles must be well-ventilated.
6. Fire Extinguishing Agents
Following fire extinguishing agents can be used to control and extinguish magnesium alloy fires.
a. Dry molten metal (aluminum oxide) has a low melting point and is particularly suitable for magnesium alloys.
b. Type D fire extinguisher.
c. Dry, oxide-free cast iron chips.
d. Dry sand.
The most effective fire extinguishing method is molten metal, which forms a molten layer on the surface of liquid magnesium, isolating it from oxygen. Die-casting shops should have sufficient supplies of molten metal. Dry cast iron chips and sand cool and extinguish fires. Because magnesium and silicon may react, sand containing silicon should not be used in crucibles containing large amounts of liquid metal. Type D fire extinguishers should only be used as an alternative, as they may disperse burning magnesium chips and spread the fire.

1. Fire Extinguishing Agents and Their Methods are as follows:
A: Magnesium Alloy Covering Agent
(a) Covering agents are usually used to extinguish fires in furnace, in the early stages of combustion, or when burning lightly.
(b) When using, scoop out the dry covering agent with a shovel or other tool and sprinkle it evenly over burning material.
(c) Never throw a plastic bag directly into a fire unless fire is too large to be approached.
B: Dry Cast Iron Sand
(a) Dry cast iron sand can be used to extinguish fires, regardless of whether fire is already burning.
(b) Before using, make sure cast iron sand is dry.
(c) When using, use a shovel to sprinkle the cast iron sand over burning material, using a large amount to evenly cover surface.
(d) When extinguishing magnesium chips or slag, not only cover them but also stir them for better extinguishing results.
C: Metal Fire Extinguisher for Magnesium Alloys (Type D Fire Extinguisher)
(a) Metal fire extinguishers cannot completely extinguish burning magnesium.
(b) Operate according to fire extinguisher's instructions and procedures. Do not use excessive pressure to prevent burning magnesium chips from spreading and causing a wider fire.
(c) Since it is impossible to completely extinguish a fire, after fire is under control, embers must be removed in small batches and shoveled to another safe location for further disposal.
D: Dry Sand
(a) Ensure dry sand is dry before use.
(b) When using, use a shovel to pile dry sand onto burning object. Amount should be large and thick, and no flames should be visible.
(c) When extinguishing magnesium chips or slag, simply cover area and do not stir it, otherwise extinguishing effect will be poor.
(d) Dry sand should not be used to extinguish fires in furnaces.
2. Understanding and Extinguishing Fires in Furnaces
a. Furnace fires can generally be categorized as fires in crucible and cracked crucibles.
b. Fires in crucible are usually caused by a lack of protective gas. Check: Is protective gas on? Is amount sufficient? Is mixing ratio correct? Is there a spare bottle? Are there any leaks in pipe joints? Is furnace lid tightly closed? Furnace lid should not be opened frequently during operation.
c. Preheat slag removal tools before cleaning. Slag removal may produce sporadic sparks, but this is not a cause for alarm.
d. If a fire occurs on liquid surface due to a lack of protective gas, immediately add a large amount of cover material and apply sufficient protective gas.
(a) If white smoke is detected in furnace, remain calm, quickly disconnect power supply, notify relevant personnel, and immediately put on protective gear.
(b) Infer extent of leak based on amount of magnesium liquid discharged from drain port or observed through inspection hole and take appropriate emergency measures. If no magnesium liquid flows from drain, immediately pour a covering agent into furnace and receiving dish. Then, use a dry ladle to scoop out some molten liquid from crucible. Continue adding several completely dry magnesium ingots to quickly solidify liquid in crucible. If amount of magnesium liquid flowing out of drain is small and silky, immediately pour a large amount of covering agent into furnace and receiving dish. Before receiving dish is full, quickly scoop out some of liquid with a dry ladle. Continue adding magnesium ingots to quickly solidify liquid.
(c) If amount of magnesium liquid flowing out of drain is large, like pouring water, immediately open furnace lid and pour in a large amount of covering agent and magnesium ingots. Simultaneously, add magnesium ingots and a large amount of covering agent to receiving dish. Add as much as you can. At this point, scooping out liquid is no longer necessary, so there's no need to waste time. Then, leave scene and monitor situation from a distance.
(d) Aluminum ingots absorb more heat than magnesium for same volume. Therefore, aluminum ingots can be considered in place of magnesium ingots for firefighting.

Magnesium alloy die-castings have great application potential in many industries, especially in automotive industry, where they enjoy a broad market and potential. Due to their significant impact on overall vehicle performance, such as lightweighting, high speed, and fuel efficiency, magnesium alloy die-castings are highly valued by automakers, leading to an annual growth rate of 20-25%.
Some typical parts, such as steering wheels and clutch housings, are trending towards magnesium alloy die-casting. While magnesium alloy die-casting carries more potential hazards than standard aluminum-zinc die-casting, level of risk is not significantly higher than that of aluminum die-casting. As long as operators follow instructions accurately, safe magnesium alloy die-casting is not a problem. Some domestic manufacturers are cautious when entering magnesium alloy die-casting industry. However, with high-quality, reliable magnesium alloy die-casting equipment, coupled with sound die-casting processes and safety measures, magnesium alloy die-casting can easily achieve success. Furthermore, magnesium alloy die-casting is a promising business.