Aluminum alloy and magnesium alloy die-casting molds work under extremely harsh conditions (high temperature molten metal, high pressure, high-speed impact, rapid cooling and heating), resulting in diverse and complex failure modes. Understanding these failure modes and taking corresponding countermeasures is key to extending life of mold, improving production efficiency and reducing costs. This article shares common failure modes and countermeasures of molds.
Following are common failure modes of die-casting molds and corresponding countermeasures:

1. Thermal fatigue cracks (cracking):
Surface of mold cavity generates alternating thermal stress due to repeated heating (molten metal injection) and cooling (demolding, spraying), resulting in network cracks (cracking) and gradually expanding and deepening. This is the most common failure mode of die-casting molds.
High-incidence areas: near gate, inner gate, core, wall thickness mutation, and stress concentration area (sharp corners, small fillets).
Impact: Crack expansion causes scratches, burrs, and dimensional deviations on casting surface, and eventually mold is scrapped.

 

2. Erosion/wear:
High-speed, high-pressure molten metal flow produces strong mechanical scouring and friction on mold cavity surface (especially runner system, ingates, and core flow surface), causing material to be gradually "cut away" and lost.
High-incidence areas: sprue sleeves, ingates, runner turns, and core flow surface.
Influence: Changes in cavity size, increased surface roughness, and deformation of runner system lead to casting size deviations, reduced surface quality, and poor filling.

 

3. Chemical corrosion/mold sticking:
Aluminum alloy: Aluminum liquid reacts with mold steel (iron) at high temperatures to form a brittle Fe-Al intermetallic compound layer, which is easily torn during demolding, causing mold surface material to be stuck ("welded"). Release agent residues may also form corrosive compounds at high temperatures.
Magnesium alloy: Although magnesium has a low affinity with iron and is less sticky, magnesium alloys are very easy to oxidize, and oxide particles may aggravate mold wear. Magnesium alloy melt may produce corrosive gases (such as HCl) in a humid environment (moisture in release agent).
High-incidence areas: cavity surface, especially in areas with high temperature.
Impact: Increased roughness of mold surface, difficulty in demolding, scratches and adhesion on casting surface, frequent mold cleaning, accelerated thermal fatigue.
4. Overall plastic deformation:
Under continuous high temperature (close to or exceeding yield strength of mold material) and high pressure, mold cavity surface or weak parts undergo permanent plastic deformation (collapse, bulging).
High-incidence areas: core, boss, and areas with thin wall thickness.
Impact: Out-of-tolerance casting size and difficulty in demolding.
5. Mechanical stress cracking:
Brittle or ductile fracture caused by unreasonable mold design (stress concentration), manufacturing defects (machining knife marks, residual stress), improper operation (premature mold closing, unbalanced ejection) or accidental overload (excessive injection pressure, flash stuck).
High-incidence areas: core root, slider wedge, ejector hole edge, mold weak parts.
Impact: mold directly cracks and is scrapped, with huge losses.
6. Wear (non-erosion):
Friction wear caused by relative movement between moving parts (slider, lifter, ejector) and guide sleeve and cavity.
High-incidence areas: slider guide surface, lifter, ejector, reset rod.
Impact: moving parts get stuck, precision decreases, flash is generated, and demolding is affected.

1. Optimize mold material selection and heat treatment:
It is recommended to use high-quality hot working die steel with high thermal fatigue resistance, high toughness, good thermal conductivity, high red hardness and resistance to temper softening. H13 (4Cr5MoSiV1) is the most commonly used and cost-effective choice. For higher requirements, choose higher performance steel (such as DIEVAR, QRO90, DAC, H11 Modified, high vanadium H13, etc.).
Heat treatment should strictly control quenching and tempering process to ensure uniform and refined microstructure (tempered martensite), achieve target hardness (usually in range of 44-52 HRC, which can be adjusted according to specific parts and failure modes).
2. Optimize mold design:
Mold design should ensure that mold as a whole and key parts (core, slider) have sufficient strength and rigidity to avoid stress concentration (using large radius transition).
Mold pouring system is designed with reasonable gate position, shape and size to guide metal liquid to fill smoothly and reduce direct high-speed impact on cavity and core. Optimize overflow tank and exhaust tank design.
Design of cooling system is top priority! Cooling system should design efficient and uniform cooling water circuits (conformal cooling) to ensure that mold temperature field is uniform and controllable to avoid local overheating or overcooling. Prioritize point cooling and conformal cooling to treat areas that are difficult to cool such as cores.
Moving parts: Ensure matching accuracy and guide length of moving parts such as sliders, inclined ejectors, ejectors, etc., and set a reasonable wear compensation structure (wear-resistant block).
3. Surface treatment:
Nitriding: gas nitriding, ion nitriding (PVD), salt bath nitriding (QPQ), etc., improve surface hardness, wear resistance, anti-sticking and certain corrosion resistance, and are the most widely used surface strengthening methods.
Physical vapor deposition: such as TiN, TiAlN, CrN, AlCrN, DLC and other hard coatings. Significantly improve surface hardness, wear resistance, erosion resistance and anti-sticking, and reduce friction coefficient. It is particularly effective in solving aluminum sticking.
Surface modification: such as laser cladding, electron beam surface alloying, etc., cladding high wear-resistant and heat-resistant materials in specific areas, which can reduce strain and thermal cracking.
Carburizing/carbonitriding: used for moving parts that require extremely high surface hardness and wear resistance. It is more commonly used in parts such as ejectors and sliders.
Polishing/mirror polishing: improve surface finish of cavity (Ra < 0.2μm or even higher), reduce adhesion of molten metal, improve demolding, and delay initiation of cracks. Therefore, in order to catch up with cycle, polishing time is often compressed. Mold development cycle should be reserved as much as possible so that mold can be polished thoroughly.
4. Strictly control die-casting process parameters:
Control of mold temperature is core control point! Use mold temperature controller to accurately control mold working temperature within a reasonable range (usually 150-250℃ for aluminum alloys and 180-300℃ for magnesium alloys), and ensure that temperature of each area is uniform, so that mold is in a relatively stable thermal equilibrium field as much as possible. Preheat fully to avoid cold mold injection. And identify key areas according to structural characteristics of product to refine temperature range and monitor it every day.
Under premise of ensuring good fluidity and filling, try to use a lower pouring temperature (650-720℃ for aluminum alloys and 640-680℃ for magnesium alloys).
In terms of injection parameters, optimize slow injection, fast injection speed and conversion point, avoid excessive impact speed and pressure under premise of ensuring filling quality, and set boost pressure reasonably.
Select a highly efficient and stable release agent, and optimize spraying time, position, pressure and spraying amount. Ensure that spraying is uniform and effective, which can both demold and cool the mold, and avoid local overcooling caused by excessive spraying. Clean residue on mold surface regularly.
Under premise of ensuring solidification of casting and cooling of mold, try to shorten cycle time to improve efficiency, but avoid excessive mold temperature.
5. Standard operation and maintenance:
Thoroughly clean residues (aluminum/magnesium slag, carbon deposits of release agent) in mold parting surface, cavity, exhaust groove, ejector hole, and cooling water channel.
Check and repair minor surface damage (such as small scratches and minor cracks) to prevent them from expanding.
Check and lubricate all moving parts (guide pillars, guide sleeves, sliders, ejector pins).
Check whether cooling water channel is unobstructed and whether flow and water temperature are normal.
Strictly follow regulations to avoid barbaric operations (such as hard knocking and forced mold closing/opening too early).
Perform maintenance regularly (every shift, every day, every week):
When machine is shut down, clean thoroughly, apply anti-rust oil, and store in a dry environment.
For vulnerable areas (gates, cores), replaceable insert structures are used to facilitate maintenance and replacement, reducing overall mold costs.

Aluminum alloy: Aluminum liquid temperature is higher (~660℃), which puts a greater heat load on mold, and thermal fatigue is the primary problem.
Aluminum and iron have a strong affinity, and problem of mold sticking/chemical corrosion is very prominent, which is main cause of failure after thermal fatigue.
Erosion problems are also significant.
Countermeasures focus on: Select excellent heat fatigue resistant materials, enhanced cooling (especially the gate area), efficient surface treatment processes (such as anti-stick aluminum coating TiAlN, CrN), strictly control mold temperature and aluminum liquid temperature, and optimize spraying process.
Magnesium alloy: Temperature of magnesium liquid is low (~650℃), heat load is relatively small, but die casting speed is usually higher (due to good fluidity).
Magnesium has weak affinity with iron, and problem of sticking is relatively mild.
It is easy to oxidize, abrasive effect of oxides aggravates erosion and wear.
There is a potential corrosion risk in a humid environment (moisture content of release agent).
Countermeasures focus on: good wear resistance (for erosion), good thermal conductivity (rapid heat dissipation), efficient cooling system, controlled oxidation (melting protection, reducing air entrapment), ensuring that release agent is dry or using low moisture/no release agent technology, and paying attention to corrosion prevention.

Extending life of aluminum alloy and magnesium alloy die casting molds is a systematic project, which requires comprehensive measures from various aspects such as materials, design, manufacturing, heat treatment, surface treatment, process control, operation and maintenance. Selecting high-quality mold steel and performing precise heat treatment is \basis. Scientific design, especially efficient and uniform cooling system is \core. Applying appropriate surface treatment technology (especially nitriding and PVD coating) is a key means to improve performance. Strict control of process parameters, especially mold temperature and spraying, is a guarantee in daily production. Standardized operation and strict implementation of maintenance system are indispensable links to extend life of molds.
Stability and control of die casting quality are core of die casting process. By taking these comprehensive countermeasures, mold failure can be significantly delayed, production efficiency can be improved, and production costs can be reduced.