This British Standard was originally issued together with BS 1003, ' High purity zinc', at the request of the Zinc Development Association in 1942 when the development of dependable zinc alloys of good mechanical properties had resulted in a rapid ,increase in the use of zinc alloy die castings for engineering purposes.
The formulation of these alloys was . the result of much research and the specified compositions were chosen as those giving the optimum balance of properties. Subsequent experience showed that some allowance should be made for loss of aluminium and magnesium during casting and in the 1955 revision of this standard therefore, their limits were slightly modified.
The presence in these alloys of certain impurities, particularly tin. lead and cadmium, the last two of which are usually found in zinc ores, may cause liability to intercrystalline corrosion with resultant dimensional instability and loss of strength. The basic zinc used for the manufacture of these alloys must therefore be such that these impurities are strictly limited.
In the 1955 revision of BS 1004 other impurities previously included under the heading traces were given definite limits, although the specification did not require an analysis to be made for these elements. This was made clear in the new layout of the chemical composition clause. Similar limits were included for the alloys, as the impurities will persist. Indium was included under this heading as investigations had shown that it might be particularly detrimental.
In 1962 BS 1003 was withdrawn as zinc of the same chemical composition was being included as grade Zn 1 of DS 3436, Ingot zinc, and an amendment to BS 1004: 1955 was issued detailing the consequent change to this specification
In this revision of BS 1004 a maximum limit has been included for nickel in the ingot alloys as this element may enter the alloys from the melting equipment and a higher maximum limit has been included in the castings to allow the limited use of plated scrap material under close control.
In addition the limits for iron in the ingot alloys have been tightened in line with ISO/R 301, Zinc alloy ingots " published in 1963.
The analytical methods previously included in BS 1005. 'Sampling and analysis of high purity zinc and zinc alloy die castings', and the polarographic methods previously included in BS 1225: 1945, arc now being superseded by methods issued as Parts of BS 3630, ' Methods for the sampling and analysis of zinc and zinc alloys '. and when the series is complete it will include methods for all elements for 'which limits arc set in BS 1004 and BS 3436, f Ingot zinc .BS 1005 will then be withdrawn. A new edition of BS 1225 has also been issued which relates to spectrographic analysis only.
Arrangements made in 1955 for the use of the BSI certification. mark in connection with this standard continue. Manufacturers who hold a license from the BSI to use this mark are required to ensure that the whole of their production of zinc alloy die castings complies with the requirements of Section 2 of BS 1004 except that permission may be given for the production of castings with a higher copper content than that specified for Alloy B of BS 1004, provided the impurity limits of Alloy B are observed. The use of material containing inserts and of plated scrap material is permitted so long as the remelt derived there-from is of such a quality that die castings made from it comply with the chemical composition set out in Section 2 of BS 1004. The patching, plugging or welding of castings is entirely disallowed.
In Appendix A the mechanical properties of pressure die cast specimens are given in SI units which are calculated equivalents of the properties given in the 1955 edition. The conversion factors used are shown in Appendix B.
The SI System of units (Systeme International d'Unites) is a newly rationalized selection of units in the metric system. involving the newton as the unit of force, which has been adopted by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC).
Recommendations on the design and production of zinc alloy pressure die castings are to be found in CP 3001, "Code of Practice for zinc alloy pressure die casting for engineering'.
