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Car keychain in chrome-plated zinc alloy versus polished aluminum alloy - 22 Apr, 2014
 
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These images show four glossy finish die cast metal car keychains in 1:87-scale.  The Porsche 959 and Ferrari F40 are made of chrome plated zinc alloy die cast, and the Lamborghini Reventon and Aventador are made of polished aluminum alloy die cast.


The chrome plated zinc alloy die cast car keychains as shown are mass-market product selling at low price.  They are well made with correct body shapes.  However, due to the constraint of production cost in order to keep the selling price low, the car body can only be slightly polished and the glossy finish is made of chrome plating.  If we enlarge the images, the coarse surface becomes obvious on the windows and the edges of the body panels.   It will require extensive manual polish to smoothen the coarse surface, but it is a process too costly for a mass-market product selling at low price.


Polishing a hard metal surface to a near perfect smooth finish is a costly process because it is labour intensive.  It also creates a high defective rate because once the surface is over-polished, the body contour deformed and the castings will be scrapped.


Zinc alloy is a material which is user-friendly with a low melting point and is easy to cast.  The steel mold used to cast zinc alloy can easily survive a million shots.  This is the reason why die cast model cars, whether in large or small scale, are predominantly cast with zinc alloy.  However, zinc alloy is a metal that can oxidize quickly, within days after casting, the surface will start to oxidize and turn greyish.  Zinc alloy model cars in glossy finish can be done in low cost by chrome plating; it cannot be a bare polished model without coating because the surface will oxidize quickly.


When comparing side by side the car models in polished aluminum and chrome-plated zinc, the polished aluminum gives the car body a unique, yet high-tech-feel glossy metal finishing that is different than the chrome-plated one.  This is why AUTOart chooses aluminum for the manufacturing of these glossy model cars.


It is very rare that a miniature model will be cast of aluminum.  The main reason is that aluminum has a higher melting point than zinc; the molten material is corrosive and often will attack the steel mold during casting. This reduces the mold life by 20 to 50 times in comparison to the zinc alloy casting.  Also, aluminum casting creates small bubbles, which get easily trapped during the casting process; this causes a very high rejection rate of the castings.


Casting aluminum cars in such a small scale (1:87 scale) can be challenging when it comes to showcasing the small details of the cars.  In order to produce the accurate contour of the car that is true to scale, the car is designed with the construction of 16 ~ 20 components despite its small scale.  All the windscreens and side windows are actually tiny chrome plated plastic parts attached individually to the main body.  This is done to give the realistic and true look of what the windscreens and windows would look like on the real car and it eliminates any surface distortions. 


The aluminum body is carefully polished by hand to a glossy finish and it is not coated with any protective layer.  This is done purposely because aluminum is a stable material under indoor condition, it will not oxidize easily.  Even after months or years that the aluminum surface starting to become dull, it can easily be buffed away using metal polishing compound.  After polishing, the product will look like new again.  Re-polishing is not possible if the product is coated with a protective layer.

Like any AUTOart model cars, the high level of finishing is unprecedented in the making of miniature car keychain.  It is not a mass-market product and the suggested retail price is US$19.90 to 29.90.  It is a collectable piece of art that you can put in your pocket and carry around with you.


 

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