Details you should know for the Quality Control of Zinc die castings

Posted on : July 7 , 2022 By  GREFEE


The zinc alloy die castings is increasingly becoming popular among zinc alloy die casting parts manufacturers. Since the requirements for the use performance are also increasing even though the physical quality of zinc alloy has been quite stable. To meet the requirements of customers, die-casting suppliers uses high-purity zinc alloy ingots with sticky process control system. In addition, the requirements for the control of smelting furnaces are also increasing, and coatings are also beginning to be widely used, the zinc alloy die casting parts manufacturers are striving to produce high-quality zinc alloy castings. 

 Introduction

Since the discovery of zinc alloy die-casting in the last century, its variety and consumption have been increasing. Moreover, an array of alloys have been produced and used in many industrial departments. Zinc alloy die casting is popular due to its multiple advantages that other die casting alloys lack, including high speed, low temperature and energy consumption, long service life. In addition, it can also be used in hot chamber die-casting machine, so the production speed is much higher than that of aluminum alloy that must be produced in cold chamber die-casting machine. The good casting performance of zinc alloy die casting molds also makes it an economical choice for the thin-walled zinc alloy die castings. The castings of zinc die-casting alloy present good casting surface, and it is easy to carry out surface processing and electroplating on it. Hence, they are quite durable.

common quality issues reported by users

Even though the quality standard of zinc alloy die-casting has been gradually unified and its composition requirements are almost the same,  the effect of die-casting alloys produced by different zinc alloy die casting manufacturers is different. The products of some die-casting manufacturers are in good quality, while others are poor. Typically, the main problems are: poor fluidity in liquid state, insufficient water leakage in the process of die casting, and more zinc slag. Some alloys also exert some adverse impacts on the surface condition of die castings, which will bring more difficulties to the following  processing, such as surface defects of die castings after polishing, electroplating defects, etc

Some of the above issued are due to the control of die-casting process parameters of die-casting manufacturers, and some of them may be resulted from the quality issues of the alloy itself, which need to be addressed specifically. It is the responsibility for producer of die-casting alloy that to improve the quality of alloys to meet the needs of die-casting producers, and also help die-casting producers adjust process parameters to make better use of their own products if under feasible conditions.

Methods to improve the quality

1. impact of main elements in zinc alloy die casting

There are aluminum, magnesium, copper, and other metals added as alloy elements in zinc alloy die casting, and the impurity elements mainly include iron, lead, tin, cadmium, etc. These elements affect the performance of the alloy to varying degrees, so they must be controlled within an appropriate range. Aluminum plays an important role in the zinc alloy. The 0.02% aluminum content in zinc can reduce the oxidation of zinc and improve the surface quality of zinc ingot, and 0.1% aluminum can inhibit the formation of fezn7 brittle compounds, lowering the brittleness of zinc ingots and the corrosion degrees of zinc on the iron mold wall. More content of aluminum will significantly improve the strength and impact toughness of the alloy. When the (AL) is 4 ~ 5%, the comprehensive properties (including strength, impact toughness and fluidity) of the alloy are the best. The elongation of zinc alloy with (AL) of 4% is 30. After further research, GREFEE found out that when (AL) exceeds 4.5%, the impact toughness of the alloy decreases a lot, but other properties remains normal. While when (AL) exceeds 5, the mechanical properties decrease and the alloy turns brittle. It indicates that  less than 3.5% aluminum will lead to poor fluidity of the alloy but high hot cracking and shrinkage. Therefore, the aluminum content should be within the range of 4.0 ~ 4.2. Magnesium, another essential addition element in zinc alloy, of which the solid solubility in zinc is close to zero. It can form hard and brittle compounds with zinc. When the content of magnesium in zinc is higher than or equal to 0.005, the strength of zinc sheet after cold rolling is enhanced, as well as the creep properties of the alloy. Besides, it is also one of the more effective elements to enhance the corrosion resistance of zinc aluminum alloy by significantly lowering the harmful effect of impurities

2 .Properly carry out pouring

The casting process after the completion of the gold smelting process is of equal significance. It adopts the pouring casting which can cause the alloy liquid to carry slag. Due to the rapid condensation in the ingot mold, the separation of slag and alloy is hard to achieve a complete effect even though there is a sag finish in the ingot, which will also slightly increase the amount of slag when using the die-casting alloy. Better casting methods avoid the formation of the platform slag layer, and try to make the process of the alloy liquid short and the drop small in the casting process

 Conclusion

Since the requirements for zinc alloy die casting have been increasing than usual, we must strive to seek method to meet the requirements and constantly improve the quality of alloy as a producer. Proper material selection and strict management of smelting process are the key. Other than that,  lower melting temperature, controlling the melting atmosphere to be neutral or reducing, using more advanced covering agent and slag, cleaning and degassing agent are more effective.

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