What are the materials the handbag hardware are made from?
The raw materials of these handbags and luggage hardware accessories are made of metals such as iron, copper or aluminum. However, most of the raw materials of luggage hardware are made of zinc alloy.
We all know that zinc alloy is more stable and less rusty than iron, and cheaper than copper and aluminum alloy.
Various decorations, such as furniture accessories, architectural decoration, bathroom accessories, lighting parts, toys, tie clips, belt buckles, various metal buckles, etc., are widely used in zinc alloy die castings, which require the quality of the surface of the castings. They must have good surface treatment properties.
So, what are the advantages and disadvantages of zinc alloy? What should we pay attention to when manufacturing zinc alloy die casting parts? Learn about them with Allwell Cast-an experienced die casting manufacturer for handbag locks, bag chains, snap hooks, etc.
What is zinc alloy?
Zinc alloy is an alloy composed of zinc and other elements added. Commonly added alloying elements include aluminum, copper, magnesium, cadmium, lead, and titanium. Zinc alloy has low melting point, good fluidity, easy to weld, braze, and plastic processing. It is corrosion resistant in the atmosphere. The residual material is easy to be recycled and remelted. However, its creep strength is low and it is easy to cause dimensional changes due to natural aging. They are processed by melting method, die-casting or pressure-processed into all kinds of metal handbag hardwares.
Zinc alloys can be divided into cast zinc alloys and wrought zinc alloys according to the manufacturing process. Cast zinc alloy has good fluidity and corrosion resistance, and is suitable for zinc alloy instrument panel, auto parts, and 5G optical module shells, etc.
Advantages and disadvantages of zinc alloy
- Zinc alloy has good fluidity, easy to weld, braze, corrosion resistance, good plasticity, and can even recycle waste materials for remelting.
- It can be used for surface treatment such as electroplating, spraying, painting, polishing, grinding, etc.
- High specific gravity, high casting performance, complex die-casting shape, thin-walled precision parts, smooth casting surface.
- Surface treatment can be carried out: electroplating, spraying, painting.
- When melting and die-casting, it will not attract iron, will not corrode the profiling, and will not stick to the mold.
- Has good room temperature mechanical properties and wear resistance.
- Low melting point, melting at 385°C, easy to die-casting.
- The creep strength is not high, and it is prone to spontaneous combustion and dimensional changes.
- There are small protruding bubbles on the surface of the die casting. Which can be discovered after die-casting, or be revealed after polishing or processing, or appear after oil injection or electroplating.
Causes of the shortcomings:
- Pores are caused by: mainly the pores and contraction mechanism. The pores are often round, and the contraction is mostly irregular.
(1) Causes of stomata:
a. In the process of filling and solidification, due to gas intrusion, pores are formed on the surface or inside of the casting.
b. Gas intrusion from paint volatilization.
c. The gas content of the alloy liquid is too high and will precipitate during solidification. The gas in the cavity, the gas volatilized by the paint, and the gas precipitated by the solidification of the alloy will eventually leave pores formed in the casting, when the mold is poorly vented.
Allwell Cast has more than 20 years of experiences as a die casting factory and surface outlook processing manufacturer. We can handle these shortcomings very well and avoid the pores.
(2) Causes of shrinkage:
a. In the process of molten metal solidification, shrinkage cavities occur due to the reduction in volume or the failure of the final solidified part to be fed by the molten liquid metal.
b. Castings with uneven thickness or partially overheating of castings cause a certain part to solidify more slowly, then the surface will form a recess when the volume shrinks. Due to the existence of pores and shrinkage holes, the water may sneak into holes during the surface treatment of the die-casting. When painting and electroplating are carried out after baking, the air and gas in the holes will be heated and get expanded; or the water in the holes will become vapor and expand in volume. This results in blistering on the surface of the casting.
- Intergranular corrosion:
Harmful impurities in zinc alloy components: lead, cadmium, and tin will gather at the grain boundary to cause intergranular corrosion. The metal matrix is broken due to intergranular corrosion, and electroplating accelerates this scourge. The affectd part will expand and lift up the coating, causing blistering on the surface of the casting. Especially in a humid environment, intergranular corrosion will cause the casting to deform, crack, or even break.
- Cracks: water pattern, cold barrier pattern, hot crack.
Water pattern and cold barrier pattern: During the filling process, the molten metal that enters first contacts the mold wall solidify prematurely, and then the molten metal enters afterwards cannot be fused with the solidified metal layer. Moiré patterns are formed at the butt of the casting surface. Striped defects appear. The water ripples mark is generally in the shallow layer on the surface of the casting; while the cold barrier may penetrate into the inside of the casting.
a. When the thickness of the casting is uneven, stress will be generated during the solidification process;
b. Premature ejection, insufficient metal strength;
c. Uneven force during ejection
d. Too high mold temperature makes the crystal grains become coarse;
e. The presence of harmful impurities.
The above factors may cause cracks.
When the die casting has water ripples marks, cold barrier marks, and hot cracks, the liquid will penetrate into the cracks and be converted into vapor during next process-baking. The pressure will lift the electroplated layer up to form blisters.
Solutions to defects:
To control the generation of pores, the key is to reduce the amount of gas mixed into the casting.
The ideal metal flow should continue to accelerate from the nozzle through the split cone and runner into the cavity to form a smooth and consistent metal flow. The tapered runner design can achieve this goal, which is, the pouring flow should be gradually reduced from the nozzle to the gate at an accelerating rate. In the filling system, the mixed air is caused by the mixing of turbulence and the metal liquid.
From the study of the simulated die-casting process in which the molten metal enters the cavity from the casting system, it is obvious that the sharp transition position and the incremental casting in the runner will cause obvious turbulence and entrain gas, and the stable molten metal is conducive to the gas entering the overflow groove and the exhaust groove from the runner and the cavity, discharging out of the mold.
For shrinkage cavity, the die-casting solidification process for all parts should happen at the same time as possible to uniformly dissipate heat and solidify. Reasonable nozzle design, inner gate thickness and location, mold design, mold temperature control and cooling can be used to avoid shrinkage.
For the phenomenon of intergranular corrosion: we need to mainly control the content of harmful impurities in the alloy raw materials, especially lead<0.003%. Pay attention to the impurity elements brought by the waste, which is the reason why Allwell Cast always use first hand new materials to make sure quality.
For water ripples lines and cold partition lines, the mold temperature should be increased properly, the gate speed can be increased properly, or the overflow groove in the cold partition area can be enlarged to reduce the appearance of cold partition lines.
For hot cracks: the thickness of the die casting should not be changed sharply to reduce stress; adjust the relevant die casting process parameters; reduce the mold temperature properly.
Allwell Cast designs and produces thousands of zinc alloy die-cast products. Cooperating with customers’ years of experience in development and production, we have rich experience in die-casting mold design, production, and appearance processing. We Can help customers get the best quality products in the shortest time.