Zinc Alloys Casting Parts Case

Zinc alloy is widely used in sanitary ware, bags, shoes, and accessories due to its convenience, plasticity, low cost and high processing efficiency.

Molds are usually made of stronger alloys, a process similar to injection molding.

Most die-casting castings are iron-free, such as zinc, copper, aluminum, magnesium, lead, tin, and lead-tin alloys and their alloys. So zinc alloy is very suitable for the die casting process of a material.

Die-Casting Zinc Alloy Materials

Zamak 3

The Zamak 3 is the most widely used zinc alloy in North America and is generally preferred for zinc die-casting for some reasons.

The required physical and mechanical properties are well balanced;

Excellent ca-stability and long – term dimensional stability;

Excellent surface treatment characteristics, suitable for electroplating, spraying and chromate treatment;

Compared with die-casting aluminum alloy, it has excellent shock absorption and vibration absorption.

The mechanical properties

Tensile Strength (MPa)Yield Strength (MPa)Shock Strength

(J)

Shear Strength

(MPa)

Hardness

(HB)

Elongation

(%)

283221582148210

Physical Property

Thermal Conductivity  (W/Mk)Density

(g/cm3)

Melting Point

(C)

Coefficient of Thermal Expansion
1136.638427.4

Chemical Composition

AlCuFe

(Max)

Pb

(Max)

Cd

(Max)

Sn

(Max)

ZnMg
3.5-4.30.250.10.0050.0040.003Bal0.02-0.05

Zamak 5

Zamak 5 is the most widely used zinc alloy in Europe.

Its copper content is higher than that of Zamak 3, so its strength is higher.

Less malleable than Zamak 3 (higher elongation).

Designers must keep in mind that ductility degradation affects form-ability during secondary operations such as bending, riveting, extrusion, or edging

Due to the abundant resources of the Zamak 3, component engineers often use design modifications instead of the Zamak 5 to enhance component strength

It is recommended to use the Zamak 5 cast when tensile properties need to be improved.

The Zamak 5 is easier to electroplate, finish, and machine than the Zamak 3.

The mechanical properties

Tensile Strength (MPa)Yield Strength (MPa)Shock Strength

(J)

Shear Strength

(MPa)

Hardness

(HB)

Elongation

(%)

32822865265917

Physical Property

Thermal Conductivity  (W/Mk)Density

(g/cm3)

Melting Point

(C)

Coefficient of Thermal Expansion
1096.638327.4

Chemical Composition

AlCuFe

(Max)

Pb

(Max)

Cd

(Max)

Sn

(Max)

ZnMg
3.5-4.30.75-1.250.10.0050.0040.003Bal0.03-0.08

Zinc Alloy Die-Casting  Features

Zinc alloy characteristics:

High strength and hardness;

Excellent conductivity;

Thermal conductivity is strong;

Low cost of raw materials;

Good dimensional accuracy and stability;

Excellent thin-walled capability;

Can be cold forming, easy to join;

High-quality surface treatment characteristics;

Excellent corrosion resistance;

Fully recyclable;

High strength and excellent hardness make zinc an ideal alternative for machining, pressing, stamping and assembly components.

Application of zinc die-casting:

The complex net – formed zinc shell is thin-walled and has excellent electrical properties and shielding properties.

With our patented multi-slider die-casting process and outstanding thin-walled capabilities, we are a leading supplier of zinc components for a wide range of consumer electronic devices

Zinc’s ca-stability, wear resistance, and structural integrity make it suitable for creating parts with multi-dimensional complex shapes for the automotive safety and electronics industries.

Advantages of Zinc Die Casting

Zinc alloy die casting is a kind of casting, zinc alloy melting point is low, good fluidity, easy to melt welding, corrosion resistance in the atmosphere, the crippled material is easy to recover and remelting;

However, the creep strength is low and the size change has been caused by natural aging. Melting preparation, die – casting or pressure processing into the wood.

Die casting is a casting method in which molten alloy is filled with a high- speed steel mold cavity and the solidified liquid of the alloy forms a casting under pressure. Die-casting methods are different from high pressure and high speed to other main features:

1. It is filled with liquid metal under pressure, and crystallizes at a relatively high solidification, usually at a pressure of 15-100mpa.

2. In the high-speed filling cavity, the liquid metal is usually 10-50m /s or more than 80m/s. The filling speed of this metal is very short, about 0.01-0.2 seconds can fill the cavity.

Different Between Aluminum Alloy and Zinc Alloy

The main difference lies in the composition, the main element of zinc alloy is zinc, generally greater than 85%, the main element of aluminum alloy is aluminum, generally greater than 87%, but specific to see the type of alloy, grade, simple understanding is zinc alloy is in zinc to add other alloy elements, aluminum alloy is also.

An alloy based on zinc and containing other elements. Zinc alloy has a low melting point, good fluidity, easy fusion welding, brazing and plastic processing, corrosion resistance in dry air and atmosphere, residue and waste easy recovery and remelting, But the creep strength is low, and the natural aging will make the size change. Zinc alloys can be divided into cast zinc alloys and deformed zinc alloys according to the manufacturing process.

The yield of cast alloys is much higher than that of deformed alloys. According to different casting methods, cast zinc alloy can be divided into pressure cast zinc alloy and gravity cast zinc alloy.

Pressure – cast zinc alloy: this alloy has developed rapidly since it was used in the automobile industry in 1940. About 25% of total zinc consumption is used to produce the alloy. The most commonly used alloy is Zn-Al-Cu-Mg.

Gravity cast zinc alloy: can be cast in a sand mold, gypsum mold or hard mold. This kind of zinc alloy not only has the characteristics of general die-casting zinc alloy, but also has high strength, good casting performance, no obvious influence of cooling speed on mechanical properties, residual and waste can be recycled, the gate is simple, is not sensitive to overheat and remelting, has small shrinkage rate, less porosity, can be electroplated, and can be refined by conventional methods.

Deformed zinc alloys: in addition to the traditional zinc alloys, Zn-1Cu-0.1Ti and Zn-22Al alloys have been used in industrial applications. After the former alloy is rolled, the dispersion particle of the TiZn15 inter-metallic compound is arranged along the rolling direction.

Zinc alloy die casting is widely used in various decorative aspects, such as furniture accessories, architectural decoration, bathroom accessories, lighting parts, toys, tie clips, belt buckles, various metal buckles, etc., so the casting surface quality requirements are higher, and at the same time requires good surface treatment performance.

The most common defect in zinc alloy die-casting is surface foaming. The defects are characterized by the appearance of protruding vesicles on the surface of die-casting, which are found after die-casting, exposed after polishing or processing, and after oil injection or electroplating.

Causes of foaming of Zinc Alloy Die Castings:

1. Hole causes:

The main mechanism is stoma-ta and contraction, stoma-ta tend to be round, and contraction is mostly irregular.

(1) causes of stoma-ta:

A. During the filling and solidification of the metal liquid, gas intrusion causes holes on the surface or inside of the casting.

B. The gas volatilized from the coating invades.

C. The alloy liquid contains too much gas and precipitates during solidification.

When the gas in the cavity, the gas volatilized from the coating, the gas solidified from the alloy, and the gas in the mold exhaust is not good, the air hole is finally left in the casting.

(2) causes of shrinkage cavity:

A. During the solidification of liquid metal, shrinkage occurs because the volume is reduced or the solidification part cannot be supplemented by liquid metal.

B. Casting with the uneven thickness or local overheating of the casting results in slow solidification of a certain part and concave position formed on the surface during volume shrinkage.

Due to the existence of pores and shrinkage holes, holes may enter the water during surface treatment of die castings. When baking after painting and electroplating, the gas in the holes is heated and expanded. Or the water in the hole will change steam, volume expansion, resulting in the casting surface bubble.

2. Inter-crystalline corrosion causes harmful impurities in zinc alloy composition: lead, cadmium, and tin will gather at the junction of grains, leading to inter-crystalline corrosion, and the metal matrix will break due to inter-crystalline corrosion.

Electroplating accelerates this scourge. Especially in the humid environment, inter-granular corrosion will make the casting deformation, cracking, and even broken.

3. Crack causes: water mark, cold mark, and hot crack.

(1) water mark and cold barrier mark: during the filling process of metal liquid, the contact wall of metal liquid that enters first solidifies prematurely, and the metal liquid that enters later cannot fuse with the solidified metal layer, resulting in overlapping marks on the surface of the casting and strip defects. Water marks are generally shallow on the surface of the casting; Cold insulation may penetrate into the casting.

(2) thermal crack:

A. When the thickness of the casting is uneven, stress is generated during solidification;

B. Premature ejection, insufficient metal strength;

C. Uneven force during ejection;

D. Too high mold temperature makes grain coarse;

E. Presence of harmful impurities.

The above factors are likely to produce cracks. When there are water lines, cold lines and hot cracks in the die casting, the solution will infiltrate into the cracks during electroplating and turn into steam during baking.

Solutions to the foaming defects of zinc alloy die castings:

1. Control the generation of pores:

The key is to reduce the amount of gas mixed into the casting. The ideal metal flow should be continuously accelerated from the nozzle through the diverging cone and the runner into the mold cavity to form a smooth and uniform metal flow.

The tapered runner design is adopted, that is, the runner should be continuously accelerated from the nozzle to the inner gate to gradually reduce, which can achieve this goal.

In the filling system, mixed with liquid mixed gases is due to turbulence and metal and form pores, from liquid metal into the cavity by the casting system in the study of simulation of die casting process, obvious sprue and increasing sharp change in the cross-section of runner, will appear the metal flow turbulence and gas volume, steady liquid metal to favour gas from the runner and the cavity into the overflow tank and exhaust slot, discharge mode.

2. For shrinkage cavity:

In the process of die casting solidification, all parts should dissipate heat as evenly as possible and solidify at the same time. Shrinkage cavity can be avoided by reasonable nozzle design, inner gate thickness and location, mold design, mold temperature control, and cooling. For inter-granular corrosion: mainly to control the content of harmful impurities in alloy materials, especially lead <0.003%. Pay attention to the impurities brought by the waste.

3. For water mark and cold mark:

Can increase the mold temperature, increase the internal gate speed, or increase the overflow tank in the cold zone, to reduce the appearance of cold insulation.

4. For thermal crack:

The thickness of die castings should not change sharply to reduce stress generation; Relevant die casting process parameters are adjusted; Lower the mold temperature.