magnesium block
10-24-2009, 08:07 PM
#41
http://www.magnesium.com/w3/forum/read.php?thread=4292
http://en.wikipedia.org/wiki/Magnesium
http://www.azom.com/details.asp?ArticleID=355
http://www.sae.org/automag/techbriefs_06-00/05.htm
http://www.magnesium-elektron.com/ab...esium.asp?ID=4
the flammability, or igniteability, of magnesium is often blown out of proportion or taken out of context. Magnesium, as in pure magnesium, is highly flammable and easily ignited when it is in powdered form, and less when in shavings. It corresponds to how much surface area of the metal is exposed to an oxider which is generally the oxygen in air. Magnesium will also burn without oxygen, it can burn in pure nitrogen gas or in carbon dioxide. and you can look most of this up on wikipedia or google,
the other thing is how much mass of magnesium there is, greater mass requires greater heat before it will burn, i suppose you could compare it to building a fire with wood- start off with small light twigs no problem but try to get a 1 foot diameter log going all by itself and it takes a lot of heat to it before it gets going on it's own.
And magnesium also has decent thermal conductivity, and in a chunk form it has to melt technically before it ignites and burns. by the time that happens with an engine block, the rest of the car is already burnt so what does it matter.
the other reason why i say out of context is people just hear magnesium and think the whole thing is 100% magnesium, it is not. It is an alloy, and i don't know off the top of my head what magnesium alloys are, probably 30-70% of Mg with aluminum as the other main component, just like for titanium. So that further reduces the flammability aspect. What you really have to watch out for are those small magnesium alloy parts used in car interiors, those are what burn in car fires that cause problems which can be unexpected. And to put it in another context, how many rims out there in racing or on street cars are magnesium? Ever hear about those flaring and burning in car fires? I really haven't.
As for engine blocks, i doubt Mg alloy block will ever be used in production because the weight savings does not justify the cost of the design and durability. Mg is at the bottom of the galvanic chart, which means it corrodes very easily. Alloying helps with that but coatings are generally required which increases cost. The biggest thing that comes to mind is the cylinder liner in contact with the Mg alloy block with coolant and heat- a perfect setup for galvanic corrosion! Engine coolant would have to be designed to handle that if even possible, plus with cast iron cylinder liners iron is much higher up on the galvanic chart furthering the galvanic problem, you could use an aluminum alloy liner but then you lose durability, and strength which would limit power output. Then there's the interface between the materials of the cylinder head and head gasket. All to save maybe 50 lbs over an aluminum block when in vehicles today that are all over 3000 lbs doesn't make sense. In a race environment where cost doesn't necessarily matter then maybe.
http://en.wikipedia.org/wiki/Magnesium
http://www.azom.com/details.asp?ArticleID=355
http://www.sae.org/automag/techbriefs_06-00/05.htm
http://www.magnesium-elektron.com/ab...esium.asp?ID=4
the flammability, or igniteability, of magnesium is often blown out of proportion or taken out of context. Magnesium, as in pure magnesium, is highly flammable and easily ignited when it is in powdered form, and less when in shavings. It corresponds to how much surface area of the metal is exposed to an oxider which is generally the oxygen in air. Magnesium will also burn without oxygen, it can burn in pure nitrogen gas or in carbon dioxide. and you can look most of this up on wikipedia or google,
the other thing is how much mass of magnesium there is, greater mass requires greater heat before it will burn, i suppose you could compare it to building a fire with wood- start off with small light twigs no problem but try to get a 1 foot diameter log going all by itself and it takes a lot of heat to it before it gets going on it's own.
And magnesium also has decent thermal conductivity, and in a chunk form it has to melt technically before it ignites and burns. by the time that happens with an engine block, the rest of the car is already burnt so what does it matter.
the other reason why i say out of context is people just hear magnesium and think the whole thing is 100% magnesium, it is not. It is an alloy, and i don't know off the top of my head what magnesium alloys are, probably 30-70% of Mg with aluminum as the other main component, just like for titanium. So that further reduces the flammability aspect. What you really have to watch out for are those small magnesium alloy parts used in car interiors, those are what burn in car fires that cause problems which can be unexpected. And to put it in another context, how many rims out there in racing or on street cars are magnesium? Ever hear about those flaring and burning in car fires? I really haven't.
As for engine blocks, i doubt Mg alloy block will ever be used in production because the weight savings does not justify the cost of the design and durability. Mg is at the bottom of the galvanic chart, which means it corrodes very easily. Alloying helps with that but coatings are generally required which increases cost. The biggest thing that comes to mind is the cylinder liner in contact with the Mg alloy block with coolant and heat- a perfect setup for galvanic corrosion! Engine coolant would have to be designed to handle that if even possible, plus with cast iron cylinder liners iron is much higher up on the galvanic chart furthering the galvanic problem, you could use an aluminum alloy liner but then you lose durability, and strength which would limit power output. Then there's the interface between the materials of the cylinder head and head gasket. All to save maybe 50 lbs over an aluminum block when in vehicles today that are all over 3000 lbs doesn't make sense. In a race environment where cost doesn't necessarily matter then maybe.
10-25-2009, 03:36 PM
#42
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"Our inline six engine offers smooth power, greater acceleration and 200 lb-ft of torque at at 2750 rpms. A number of pioneering technologies make it possible. An electronically controlled water pump helps increase power output. Our patented Valvetronic system offers better fuel efficiency. And to save weight, we used a groundbreaking innovation that BMW was the first to use in a production car - an engine block made of a lightweight composite magnesium/aluminum."
BMW has been using it in production in its best selling car since '06.
Last edited by Bimmer Tech; 10-25-2009 at 03:37 PM. Reason: Addition
10-26-2009, 12:48 PM
#43
i know bmw has had a Mg block,
let me rephrase and say i doubt a Mg block will be used by all manufacturers for all engines made anytime in the near future.
check out link below for the tech stuff on the bmw mg block,
it describes how the Mg alloy components are only comprising the shell of the block, the coolant jackets and inner block where the cylinder liners are cast aluminum,
and if i read it right weight savings is only 22 lbs over the previous non-magnesium block.
BMW has never made an inexpensive car, which is fine, but i seriously doubt other manufacturers are going to follow suit and invest into the design and production of a Mg alloy block "shell" to save what i'd say is minimal weight. and the BMW Mg-block is an inline-6, weight savings would be less on an inline-4 further increasing the cost-to-weight saved ratio, and on V-6 and V-8 engines it may not even be practical or feasible to design a Mg alloy shell for the block.
http://www.mwerks.com/artman/publish...nter_960.shtml
let me rephrase and say i doubt a Mg block will be used by all manufacturers for all engines made anytime in the near future.
check out link below for the tech stuff on the bmw mg block,
it describes how the Mg alloy components are only comprising the shell of the block, the coolant jackets and inner block where the cylinder liners are cast aluminum,
and if i read it right weight savings is only 22 lbs over the previous non-magnesium block.
BMW has never made an inexpensive car, which is fine, but i seriously doubt other manufacturers are going to follow suit and invest into the design and production of a Mg alloy block "shell" to save what i'd say is minimal weight. and the BMW Mg-block is an inline-6, weight savings would be less on an inline-4 further increasing the cost-to-weight saved ratio, and on V-6 and V-8 engines it may not even be practical or feasible to design a Mg alloy shell for the block.
http://www.mwerks.com/artman/publish...nter_960.shtml
