When you enter the wonderful world of Märklin and begin to get even a little serious about these trains, you will also become acquainted with an illness afflicting earlier metal locomotives and rolling stock. This horrible disease is called Zinkpest in German and zinc pest or plague in English. Unfortunately, there is no cure. Here’s some background.

    Between 1935 and 1942 the zinc alloys used for die casting did not have the high purity necessary to make high quality castings. The high purity materials being set aside for military applications. In addition, analysis methods were not that accurate, especially at the foundries making the castings.

    Zinc pest is a form of intercrystalline corrosion. The process is accelerated by the presence of moisture in warm air. Relative humidity of 65 percent and greater accelerates the process. In alloys not meeting strict purity standards, such as those that might be set by standards organizations, hydrogen (from the water) concentrates at the grain boundaries. This results in a cracking along the grain boundaries. It is very important that old Märklin metal models not be thermally stressed. It is especially important not to subject these models to the rigors of shipment since this can involve potential temperature extremes.

    It is not possible to say with certainty that all pre-World War 2 models will suffer zinc pest. There are some pre-war models that do not show any signs of this malady. Some models have damaged frames but do have damaged superstructures. After the war from about 1945 to 1949, there was a zinc pest problem with some models but most of them from that period are not affected.

    Since then zinc die casting has undergone considerable improvement and the alloys meet much higher purity levels. Märklin uses exclusively the alloy Zamak Z 410 produced by Metallgesellschaft in Frankfurt am Main, Germany.

    With some research, I found a short technical review about zinc die casting alloys on the Internet. I paraphrase from "ZAMAK: Zinc Alloys With Great Design Flexibility and Cost Effectiveness."

    "ZAMAK 5 alloy casting, which is widely used in Europe, has the highest impact strength, approximately 10% higher tensile strength, but is less ductile than ZAMAK 3 alloy casting due to an addition of 1% copper. The fact that the ZAMAK 3 alloy is widely available and costs less than ZAMAK 5, a design modification to strengthen a part using ZAMAK 3 alloy is often recommended, instead of using the ZAMAK 5 alloy with a higher strength." While these alloys are not ZAMAK 410, they are for all practical purposes the same. The properties of ZAMAK 410 will not differ markedly from ZAMAK 3 and 5.

    Freight cars made between 1947 and 1955 and the tenders of the locomotives F 800, G 800, HR 800 and SK 800 can sometimes show corrosion of the magnesium die castings. This white crystalline corrosion product is evidence that the composition and casting process were not optimal. It was known at the time that these particular alloys did have some tendency to corrode but that this could be controlled by proper painting. Corrosion set in under humid conditions. These freight cars and tenders used two different die casting alloys. The superstructure was the magnesium alloy and the frame used a zinc die casting alloy.

Koll’s Preiskatalog 1997, page 22.

"ZAMAK: Zinc Alloys With Great Design Flexibility and Cost Effectiveness" by Ed Wijaranakula, 1998, Infotix Systems.